Activity #4: Chemical Bonds

Vocabulary Covalent bond Chemical bond Reactants Stable/unreactive Products Unstable/reactive Valence level Charge Octet rule Chemical equation HONC Law of conservation of matter Reactivity

Chemical Bonds Atoms in compounds are held together by chemical bonds Making bonds involves the electrons that surround each nucleus Electrons that are available to form bonds are called valence electrons

Valence Electrons Electrons of an atom are spread out in different layers around the nucleus to make an “electron cloud” Layers are called energy levels 2 electrons go in the first energy level 8 electrons can go in the second energy level and beyond (octet rule)

Valence Electrons If there are not 8 electrons for the outer level, these empty spots are called vacancies and some electrons are unpaired Unpaired electrons in the outer layer are the valence electrons Valence electrons can pair with those from other atoms to “fill” the vacancy Creates a molecule

Bohr Model vs. Lewis Dot Structure Lewis Dot Structure: shows just the valence electrons in the outer energy level Bohr Model: shows all of the electrons in their energy levels

Practice Element Bohr Lewis Dot Carbon   Nitrogen

Reactive vs. Stable Reactivity of an atom is determined by the number of vacancies in its outer energy level If there are vacancies, the atom is reactive/unstable If there are no vacancies, the atom is nonreactive/stable If the vacancies are filled due to bonding, the molecule is stable

Types of Chemical Bonds 1. ionic bonds 2. covalent bonds There are other types of bonds and interactions but they are not as strong

Ionic Bonds Formed when one or more electrons are transferred from one atom to another Atom that loses electrons becomes positively charged Atom that gains electrons has a negative charge These positively and negatively charged atoms are known as ions These oppositely charged ions have a strong attraction for each other, forming an ionic bond

Covalent Bonds Electrons are shared by atoms instead of transferred Moving electrons travel about the nuclei of both atoms, forming a covalent bond.

A covalent bond can be a… Single Covalent Bond: atoms share 2 electrons (1 pair) Double Covalent Bond: atoms share 4 electrons (2 pairs) Triple Covalent Bond: atoms share 6 electrons (3 pairs)

HONC This is the number of bonds each of these can form! H O N C 1 2 3 4   Bonds between the most important biological atoms will be covalent Number of bonds each can make is important for the compounds that will be created using these atoms Hydrogen -can form 1 bond Oxygen- can form 2 bonds Nitrogen- can form 3 bonds Carbon- can form 4 bonds

Ionic vs. Covalent Video Quiz

Chemical Reactions Chemical Reactions: process that changes or transforms one set of chemicals into another set of chemicals Involves changes to the chemical bonds that join atoms in compounds Reactants: elements or compounds that enter into a chemical reaction Products: elements or compounds produced by a chemical reaction HINT: Reactants react to produce products! Bonds of the reactants are broken and new bonds form in the products

Chemical Equations What process is this equation for? Cellular Respiration Chemical Equation: a mathematical representation of a chemical reaction Shows the numbers and types of compounds involved 6O2 + C6H12O6  6CO2 + 6H2O + ___ ATP Reactants Products

Balancing Chemical Equations The Law of Conservation of Matter: matter (atoms and elements) in a chemical reaction cannot be created or destroyed Only the arrangement of the atoms is changed, NOT the number or types Both sides of a chemical equation must be “balanced” (have the same number of atoms)

Practice Are these equations balanced? C + 2H2 --> CH4   C + 2H2 --> CH4 Na2SO4 + CaCl2 --> CaSO4 + NaCl C2H6 + O2 --> CO2 + H2O 2Al2O3 --> 4Al + 3O2 Yes No No Yes