CHEMICAL REACTIONS & CHEMICAL BONDING

ATOMS, MOLECULES, & COMPOUNDS Atoms- smallest part of an element. Molecule- two or more elements chemically combined. Same or different type of atom. ie.- O2, H2, H2O, CaCO3 Compound- two or more different types of atoms chemically combined. ie.- H2O, CaCO3, H2SO4

MOLECULES & COMPOUNDS

- Atoms want to fill their outer shell with 8 electrons. - Electrons in the last (outermost) shell are called valence electrons. - Atoms will continue to react with one another until their outer shell is full. - Valence electrons let atoms bond with other atoms.

VALENCE ELECTRONS

- The only exception to this rule is Hydrogen & Helium since their outer shell only holds 2 electrons. Molecules can bond and “unbond” by atoms being re-arranged in different combinations. - Chemical formula- (recipe), a combination of symbols that represent the elements in a compound.

FORMING CHEMICAL BONDS

WRITING CHEMICAL FORMULAS To Write a Formula: 1. Write the symbols of the substances to be bonded. 2. Indicate the oxidation number of each substance. 3. Determine what multipliers are needed to equalize the charge. 4. Write the multiplier after each substance. 5. Write the positive substance first, the negative one second. Example: Calcium and Nitrate 1. Calcium - Ca; nitrate = NO3 2. Ca = +2; NO3 = -1 3. Because 2 X -1 = 2, The multiplier for this formula is 2. 4. The subscripts are 1 and 2; Ca, and (NO3)2. 5. Ca (NO3)2 , or calcium nitrate.

CHEMICAL REACTIONS - Also known as a chemical change. Occur when chemical bonds are formed or broken. yields 2Mg + O2 2MgO reactants product

CHEMICAL EQUATIONS

EVIDENCE OF A CHEMICAL REACTION: - Color change - Precipitate forms - Gas produced - Temperature change - Properties change.

CLASSIFICATION OF CHEMICAL REACTIONS: Synthesis- “put together,” builds compounds from simpler substances. A + B AB Decomposition- breaks down compounds into simpler substances. AB A + B

EXAMPLES: Replacement- one element replaces another element in a compound. Single- AB + C AC + B A + BC AB + C Double- AB + CD AC + BD

CONTROLLING CHEMICAL REACTIONS: Every chemical reaction involves a change of Energy. Exothermic- releases energy in the form of heat. Endothermic- reaction takes energy from the solution, to make it feel cool.

ENDOTHERMIC REACTIONS - endo- to the inside. - therm- heat. Reaction must take in Energy from its surroundings to occur. Energy is absorbed in the form of heat, electricity, light, etc.

EXOTHERMIC REACTIONS - exo- to the outside. - therm- heat. Energy is released as heat, light, and sound.

ACTIVATION ENERGY Minimum amount of energy needed that has to be added to start a chemical reaction. - This gets the reaction started.

ACTIVATION ENERGY Energy is needed to begin a chemical reaction.

RATE OF CHEMICALREACTIONS Depends on how easily the particles of the reactants can get together; it is affected by: - Concentration - Surface area - Temperature - Catalyst - Inhibitors

IONIC BONDING Ion is a positively or negatively charged atom. Ions are created when an atom gains or loses an electron when they form a bond. Attraction between two oppositely charged ions. “Opposites attract”. - Compounds are electrically neutral.

ATTRACTION NEEDED TO FORM SALT

SALT- A BOND BETWEEN A METAL & A NON-METAL

FORMING AN ION

PROPERTIES OF IONIC BONDS - Forms very strong bonds. - Dissolves in water. - Often a solid at room temperature. - Shatters or breaks, instead of bending. Polyatomic ions- group of atoms that acts as one. Example- (CO3)-2 (OH)-1

SALT IN SOLUTION Salt (NaCl) forming Na+ and Cl- ions

IONIC BONDS - Naming Ionic Bonds: + ions (usually a metal) come first, followed by the - ion. If the - ion is an element, it will end with the letters -ide. example: NaCl Sodium chloride If the - ion is a polyatomic ion the ending remains the same. example: CaCO3 Calcium carbonate

FORMULAS FOR IONIC COMPOUNDS

COVALENT BONDING Formed when electrons are shared between atoms. - Bond between 2 non-metals. Both atoms attract the shared electron at the same time. - Can form double & triple bonds.

COVALENT BONDS

COVALENT BONDING

COVALENT BONDS Valence electrons Single bonds Double & Triple bonds

POLAR/NON-POLAR COVALENT BONDS Polar bonds- some atoms pull stronger on shared electrons than others. As a result, electrons move closer to one atom,causing the atom to have a slight electric charge. Non-polar bonds- pull on the atoms equally.

Since water is a polar molecule it attracts the Na+ and Cl- ions.

WATER- A POLAR COMPOUND

PROPERTIES OF COVALENT BONDS - Often a liquid or gas at room temperature. - Most don’t form crystals. - Low melting temperature. - Low boiling temperature. - Poor conductors of electricity.

FORMULAS FOR COVALENT COMPOUNDS