# 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:

- 

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

- 
- 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**==.

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## 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**.

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### 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.


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