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title: 8th Grade S1T2 Science Final Exam Notes

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# 8th Grade S1T2 Science Final Exam Notes
## Chapter 4 - Atoms and Bonding
 - Valence electrons
     - ==**Valence electrons**== of an atom are the outermost electrons, which have the highest energy. 
     - The number of valence electrons helps determine the ==**chemical properties**== of that element. 
     - Valence electrons are involved in ==**chemical bonding**==. 
 - Drawing Bohr Models
     - Level 1 (closest to the nucleus) can hold a **maximum of 2 electrons**. 
     - Level 2 and Level 3 can hold a maximum of 8 electrons. 
     - You must fill one level before going to draw the next level. 
 - Bohr Diagrams - Carbon
     - **Carbon** has **6** electrons. 
     - The first shell can ***hold only 2*** electrons. 
     - Since you already have 2 electrons, you need to add 4 more. 
     - These go in the 2^nd^ shell. 
 - Electron Dot Diagrams
     - Different elements can have from **1-8** valence electrons. 
     - An ==**electron dot diagram**== or a ==**Lewis Dot Structure**== includes the symbol for the element surrounded by dots. 
     - Each dot stands for **one** valence electron. 
 - Bonding
     - Atoms tend to form bonds so that they have **8** valence electrons and become more stable. 
     - When atoms bond, valence electrons may be ==**transferred**== or ==**shared**==. 

     - Na Cl => Na^+^ Cl^-^ => ==transferred==
     - H~2~ + O => H~2~O => ==shared==

     - A ==**chemical bond**==, is the force of attraction that holds the atoms together as a result of the arrangement of electrons between them. 
 - Metals
     - Metals atoms react by **losing** their valence electrons. 
     - In general, the ***reactivity of a metal depends on how easily its atom lose valence electron***. 
     - The reactivity of metals **decrease** from left to right across the periodic table. 
 - Alkali Metals
     - Group 1
     - Atoms of the alkali metals have **1** valence electrons. 
     - When an alkali metal **loses** an electron, it is left with a full outer shell. 
     - Because of this, alkali metals are ***very reactive***. 
 - Nonmetals
     - The nonmetals usually combine with metals by **gaining electrons**. 
     - Nonmetals can also combine with other nonmetals and metalloids by **sharing electrons**. 
 - Halogens
     - Group 17
     - Halogens have **7** valence electrons. 
     - **Gaining** one more electron gives these atoms a full outer shell. 
     - Because of this, halogens are ***very reactive***. 
 - Noble Gases
     - Group 18
     - Atoms of the noble gases have **full shell** and therefore, ***do not react easily*** with other elements. 
 - Metalloids
     - Atoms of the metalloids can either **lose / share** electrons when they combine with other elements. 
     - Each metalloid has some of the properties of metals and some of the properties of nonmetals. 
 - Hydrogen
     - Hydrogen is in group 1 in the periodic table because it has **1 valence electron** but it's a nonmetal. 
     - It **share** it electrons when forming compounds with other nonmetals to obtain a stable arrangement of 2 electrons. 
___

### **Lesson 2 - Ionic Bonds**
 - Ions
     - An ==**ion**== is an atom or group of atoms that has electric charge (Positive / Negative charge). Protons =/= Electrons. 
     - ==**Cation**== - a positive ion. 
     - ==**Anion**== - a negative ion. 
 - Metals and Nonmetals
     - Because a stable atom has ***8 valence electrons***. 
     - **Metals** atoms are likely to ***lose electrons***. 
     - **Nonmetals** atoms are likely to ***gain electrons***. 
 - Write Ions and their charges

| Name | Charge | Symbol or Formula | 
| ---- | ------ | ----------------- | 
| Lithium | 1^+^ | Li^+^ | 
| Sodium | 1^+^ | Na^+^ | 
| Potassium | 1^+^ | K^+^ | 
| Ammonium | 1^+^ | NH~4~^+^ | 
| Calcium | 2^+^ | Ca^2+^ | 
| Magnesium | 2^+^ | Mg^2+^ | 
| Aluminum | 3^+^ | Al^3+^ | 
| Flouride | 1^-^ | F^-^ | 
| Chloride | 1^-^ | Cl^-^ | 
| Iodide | 1^-^ | I^-^ | 
| Bicarbonate | 1^-^ | HCO~3~^-^ | 
| Nitrate | 1^-^ | NO~3~^-^ | 
| Oxide | 2^-^ | O^2-^ | 
| Sulfide | 2^-^ | S^2-^ | 
| Carbonate | 2^-^ | CO~3~^2-^ | 
| Sulfate | 2^-^ | SO~4~^2-^ | 

---

Give one valence electron is easier. 
Give 4 usually share valence electrons. 
H^+^ => already given valence electron. 
Hydrogen ion => H^+^
Hydrogen atom => H
Hydrogen anion => H^-^

 - Polyatomic Ions
     - ==**Polyatomic ions**== are ions that are made of more than one atom. 
 - Ionic Bond
     - An ==**ionic bond**== is the attraction between two oppositely charged ions. 
     - The resulting compound is called an ==**ionic compound**==. => **The result of ionic bonding**. 
 - Sodium Atoms + Chlorine Atoms
     - Sodium has **1** valence electron and chlorine has **7**. 
     - The valence electron from Sodium is ***transferred*** to Chlorine. 
     - Both atoms become ions. 
     - Sodium become a ***cation*** (Na^+^) and Chlorine becomes an ***anion*** (Cl^-^) 
 - Formulas and Names of Ionic Compounds
     - A ==**chemical formula**== is a group of symbols that shows the ratios of elements in a compound. 
     - Example: The charge on the Magnesium ion is 2^+^ and the charge on each Bromine ion is 1^-^. 
     - The two Bromine ions ==***balance***== the charge on the Magnesium ion. 
     - The number 2 in the formula is a **subscript**, which tells the ratio of elements in a compound. 
     - The ratio of Magnesium ions to Bromine ions in MgBr~2~ is **1 to 2**. 
     - To write the formula for an ionic compound, write the symbol of the **cation** and then the symbol of the **anion**. 
     - Add the **subscripts** that are needed to balance the charges. 
 - Copy the Formulas and Names of Ionic Compounds

| Cation | Anion  | Compounds | 
| ------ | ------ | --------- | 
| Ca^2+^ | Cl^1-^ | CaCl~2~   | 
| Ba^2+^ | O^2-^  | BaO       | 
| K^1+^  | S^2-^  | K~2~S     | 

 - Naming Ionic Compounds
     - The cation always goes first and it's name ***doesn't change***. 
     - The anion goes second and it's name usually ends in ==**ide**== (if it is one element. ) 
     - Ex. 
         - Nitrogen => Nitride
         - Oxygen => Oxide
         - Flourine => Flouride
         - Phosphorous => Phosphide
         - Sulfur => Sufide
         - Chlorine => Chloride
         - Bromide => Bromide
         - Iodine => Iodide
 - Practice: 
     - NaCl : Sodium Chloride
     - MgO : Magnesium Oxide
     - BeF : Beryllium Flouride
 - Properties of Ionic Compounds
     - Ionic compounds: 
         - Form **crystals** - an orderly 3D arrangement. 
         - Are **hard** and **brittle**. 
         - Have **high melting points**. 
         - **Conduct electric current** when dissolved in water / melted. 

___

### Lesson 3 - Covalent Bonds
 - Covalent bonds: 
     - The chemical bond formed when two atoms **share electrons** is called a ==**covalent bond**==. 
     - Covalent bonds usually form between ***nonmetal bonds***. 
     - Ionic bonds usually form when a metal combines with a nonmetal. 
 - Electron Sharing
     - In the example below, sharing electrons gives each flourine atom **8** valence electrons. 
     - The two bonded flourine atoms form a ==**molecule**==, which is a ***neutral*** group of atoms joined by **covalent** bonds. 
 - How many bonds? 
     - A ==**double bond**== forms when two atoms share two pairs of electrons. 
     - A ==**triple bond**== forms when atoms share three pairs of electrons. 
 - Properties of Molecular Compounds
     - A molecular compound is a compound that is made up of molecules, which are covalently bonded. 
     - For example, water is a molecular compound with two covalent bonds. 
         - Each hydrogen atom ***shares one pair*** of electrons with an oxygen atom. 
     - Molecular compounds: 
         - Usually ***do not conduct electric current*** when melted or dissolved in water. 
         - Have ***lower melting points and boiling points*** than ionic compounds. 
 - How do Bonded Atoms Become Partically Charged? 
     - Atoms of some elements pull **more strongly** on the shared electrons of a covalent bond than do atoms of other element. 
     - ***Unequal sharing of electrons*** causes covalently bonded atoms to have slight **electric charges**. 
 - ==***Non-polar Bonds***==
     - A covalent bond in which electrons are shared equally is a ==**non-polar bond**==. 
 - ==***Polar bonds***==
     - When electrons are shared **unequally**, the atom with the **stronger pull** gains a slightly **negative charge**. 
     - The atom with the **weaker pull** gains a slightly **positive charge**. 
     - A molecule is polar if it has a positive charged end and a **negative charge** end. 
     - A covalent bond in which electrons are shared unequally is a ==***polar bond***==. 
 - Attractions Between Molecules
     - Opposite charges attract. 
     - Polar molecules are connected to each other by weak attractions between their slight negative & positive charges is called ==***van de waals forces***==. 
 - Rules of Drawing Lewis Structures
     - Count the total number of **valence electrons**. 
     - If the compound contains carbon, place carbon in the ***center***. 
     - Distribute the electrons so that each element has ***8 electrons*** total (except Hydrogen, which will have 2. ) 
     - Unshared electrons must be in pairs. Each pair is called a ==***lone pair***==. 
     - Check your work. 

___

### Lesson 4 - Bonding in Metals
 - What is the Structure of a metal crystal? 
     - A metal crystal is composed of closely packed, **positively charged** metal ions. 
     - The **valence electrons** drift among the ions. 
     - Each metal ion is held in the crystal by a **metallic bond**, which is an attraction between a **positive metal ion** and the **electrons** surrounding it. 
 - What Are the Properties of Metals? 
     - Properties of metals include: 
         - A shiny ==**luster**==. 
         - High levels of ==**malleability**==. 
         - High levels of ==**ductility**==. 
         - High levels of ==**electric conductivity**==. 
         - High levels of ==**thermal conductivity**==. 
 - Luster
     - The luster of a metal is due its **valence electrons**. 
     - When light strikes these electrons, they **absorb** the light and then **re-emit** the light. (put it back out. ) 
 - Malleability and Ductility
     - ==**Ductility**== - metals can be pulled into thin wires. 
     - ==**Malleability**== - metals can be rolled in to thin sheets and beaten into complex shapes. 
     - Metals act this way because the positive metal ions are attracted to the loose electrons all around them. 
     - The atoms are able to roll past each other into new positions ***without breaking the metallic bonds***. 
 - Conductivity
     - Metals conduct heat easily because the valence electrons within a metal are **free to move**. 
     - Electrons in the **warmer** part of the metal can transfer energy to the **cooler** part of the metal. 
     - ***Charged particles*** that are free to move can conduct an electric current. 
     - Metals conduct electric current easily because the valence electrons in a metal can move freely among the ions. 
 - Alloys
     - An alloy is a mixture made of two or more elements, at least of which is a **metal**. 
         - Example: 
             - Pure gold is shiny, but it's ***soft & easily bent***. For that reason, gold jewelry is made of an alloy of gold mixed with a harder element, such as **copper / silver**. 

___

## Chapter 5 - Chemical Reactions

### Lesson 1 - Observing Chemical Change
 - Matter
     - Matter is anything that has mass and takes up space. 
 - Properties of Matter
     - Matter is often described by its properties, or characteristics, and how it changes. 
     - Tow kinds of properties of matter - ***physical & chemical*** properties. 
     - A ==**physical property**== is a characteristic of a substance that can be observed **without changing** the substance into another substance. 
     - Ex. Melting point, color, texture, density, and conductivity. 
     - A ==**chemical property**== is a characteristic of a substance that describes its ability to change into other substances. 
     - Ex. Flammability, tarnishing, rusting...
 - Changes in Matter
     - **Physical Change** - alters the form or appearance of a material but doesn't make the material into another substance. 
     - A substance that undergoes a physical change is **still the same substance** after the change. 
 - Examples of Physical Changes
     - ***Change of state***
         - Ex. Melting, Freezing, Evaporating. 
     - ***Change in shape or form***
         - Ex. Bending, Crushing, Dissolving, Breaking, Chopping, Peeling, Sculpting, Filtering, and Sanding. 
 - What happen to a substance in a chemical change
     - ==**Chemical Change**== - one or more substances combine or break apart to form new substances. 
     - A chemical change produces **new substances with new & different properties**. 
 - Bonding and Chemical Change
     - Chemical change happen when ***existing bonds break and new bonds form***. 
     - As a result **new substances are produced**. 
     - Atoms form bonds when they **share or transfer** electrons. 
     - ==**Magnesium Oxide**==, a white powder, has properties that differ from those either shiny magnesium or invisible oxygen gas. 
 - Identifying Chemical Reactions
     - ==**Chemical Reaction**== involve changes in **properties** and changes in **energy** that you can often observe. 
 - Evidence of Chemical Reactions
     - Formation of Precipitate. 
     - Gas production. 
     - Color change. 
     - Physical properties such as **texture & hardness** can also change in a chemical reaction and are easy to recognize. 
     - The only sure evidence of a chemical reaction is that **one or more new substance are produced**. 
 - Changes in Energy
     - ==***Chemical Reactions***== occur when bonds break and new bonds form. 
     - ==***Breaking Bonds***== between atoms or ions **requires** energy, while **forming bonds release** energy. 
     - In an ==***exothermic reaction***==, the energy released as the product form is greater that the energy required to break the bonds of the reactants. 
     - The energy is usually released as **heat**. 
     - In an ==***endothermic Reaction***==, more energy is required to break the bonds of the reactants than is released by the formation of the products. 
     - The energy can be **absorbed** from nearby matter. 
     - When the energy is absorbed, it causes the surroundings to be **cooler**. 
     - Others need **constant heat** ex. frying an egg. 

___

### Lesson 2 - Describing Chemical Reactions

 - What Information Does a Chemical Equation Contain? 
     - A ==**chemical equation**== is a way to show a chemical reaction, using symbols instead of words. 
         - Ex. 
             - 2H~2~ + O~2~ => 2H~2~O
 - Structure of an Equation
     - The substances at the beginning are called the ==**reactants**==. 
     - When the reaction is complete, you have new substances, called the ==**products**==. 
 - How is Mass Conserved During a Chemical Reaction? 
     - ==***The law of conservation of mass***== states that during a chemical reaction, matter is not created or destroyed. 
     - In a chemical reaction: 
         - All of the atoms present at the start of the reaction are present at the end of the reaction. 
         - But they **may be rearranged to form new substances**. 
 - Open & Closed Systems
     - In an ==**open system**==, matter can enter from or escape to the surroundings. 
     - In an ==**closed system**==, matter doesn't enter or leave. 
 - Balancing Chemical Equations
     - The total number of atoms of each element in the reactants must ***equal*** the total number of atoms of each element in the products. 
     - Steps for balancing chemical equations: 
        1. Write the equation. 
        2. Count the number of atoms of each element on each side of it. 
        3. Use coefficient to balance atoms. 
         - A coefficient is a number placed in front of a chemical formula in an equation. 
        4. Look back and check your work!!! 

___

### Controlling Chemical Reactions

 - How do Reactions get started? 
     - ==**Activation Energy**== is the smallest amount of energy needed to start a chemical reaction. 
     - ***All chemical reactions*** need a certain amount of activation energy to get started. 
 - Graphing Changes in Energy
     - The **peak** on the graph shows the activation energy. 
     - At the end of an exothermic reaction, the products have less than the reactants. 
         - Graph: 

 - ![](https://i.imgur.com/Nn0d417.jpg)

     - A the end of an endothermic reaction, the products have more than the reactants. 

 - ![](https://i.imgur.com/0qrxosB.jpg)
 - What Affects the Rate of a Chemical Reaction? 
     - Surface Area
         - If you break a solid into more pieces, more particles exposed to the surface and the reaction happens **faster**. 
     - Temperature
         - When you **heat up** a substance, the particles move faster. 
         - Faster particles have more energy, which increase the speed of the chemical reaction. 
     - Concentration
         - This is the **amount of substance** in a given volume. 
         - Increasing the concentration of reactants provides more particles to react. 
     - Catalyst and Inhibitors
         - A ==**catalyst**== increases the reaction rate by lowering the activation energy needed. 
         - The cells in your body contain biological catalysts called ==**enzymes**== which help reactions occur in your body. 
         - A material used to decrease the rate of a chemical reaction is an ==**Inhibitor**==. 

___

## Chapter 6.3 - Acid and Bases
 - What Are the Properties of Acids? 
     - ==**Acid**== are substances that state sour, react with metals and carbonates, and turn blue litmus peper red. 
         - Ex.s. of acids: 
             - Hydrochloric acid in your stomach helps with digestion. 
             - Sulfuric acid drives many types of batteries. 
             - Phosphoric acid is used to make plant fertilizers. 
 - Reactions with metals
     - Acids react with certain metals to produce ==**hydrogen gas**==. 
     - When they react, the metals seem to **disappear in the solution**. 
     - Acid are described as **corrosive**, meaning they wear away other materials. 
 - Reactions with carbonates
     - Acid react with ==**carbonate ions**==. (CO~3~^2-^) 
         - Objects that contain carbonate ions: 
             - Seashells, eggshells, and chalk. 
 - Sour Taste
     - Citrus fruits, such as lemons, grapefruit, and oranges all contain citric acid, which is why they taste sour. 
 - Reactions with Indicators: 
     - An indicator is a compound that **changes color when it comes in contact with an acid**. 
     - Acids turns **blue litmus paper red**. 
 - What Are the Properties of Bases? 
     - ==**Bases**== are substances that taste bitter, feel slippery, and turn red litmus paper **blue**. 
         - Ex. 
             - Ammonia is used in fertilizers and household cleaners. 
             - Baking Soda (Sodium Bicarbonate), causes baked goods to rise. 
 - Bitter Taste
     - Foods that contain bases include **almouds and cocoabeans**, causing them to taste bitter. 
 - Slippery Feel
     - The Slippery feeling of **soaps and shampoo** is a property of the bases it contains. 
 - Reaction of Bases
     - Bases don't react with metals or carbonates. 
     - Bases can react with acids in a type of chemical reaction called ==**neutralization**==, in which both deactivate one another and form salt and water. 
 - Reactions with Indicators
     - Bases turn **red litmus paper blue**. 

___

### Lesson 4 - Acids and Bases in Solution
 - Acids in Solution
     - In a solution with water, most acids sparate into ==**hydrogen ions and negative ions**==. 
     - A ==**hydrogen ion (H^+^)**== is an atom of hydrogen that has lose its electron. 
     - Ex. ==**hydrochloric acid (HCl)**== decomposes into **hydrogen ions & Chloride ions**. 
 - Strong Acid v.s. Weak Acids
     - The strength of an acid refers to **how well the acid separates into ions in water**. 
     - In a ==**strong acid**==, molecules separate to form hydrogen ions in solution. 
     - In a ==**weak acid**==, few molecules separate to form hydrogem ions in solution. 
 - Bases in Solution
     - When soomme bases dissolve in water, they separate into ==**positive ions and hydroxide**==. 
     - A ==**hydroxide (OH^-^)**== is a negative ion made of oxygen and hydrogen. 
 - Measuring pH
     - The pH scale indicates **how acid or basic a substance is**. 
         - The pH scale expresses the concentration of ==**hydrogen ions**== in a solution. 
         - The most acidic solutions have a **high** concentration of hydrogen ions and are found at the **low** end of the scale. 
         - The most basic solution have a **low** concentration of hydrogen ions and are found at the **high** end of the scale. 
 - Neutralization
     - In a neutralization reacion, **an acid reacts with a base to produce a salt and a water**. 
     - A ==**salt**== is any ionic compound that can be made from a neutralization reaction. 

![](https://i.imgur.com/o8cE1PI.jpg) 

Review Sheet: 
[Google Document](https://docs.google.com/document/d/1YK9f7McgvR-5TXLVqGL0haL8uhLCiKp5tPZ7TozsJD4/edit?usp=sharing)