Chemical Bonds

Atom – the smallest unit of matter “indivisible” Helium atom

“Cat-Eye-On” “An-Eye-On” NEGATIVE POSITIVE ION CATION ANION An atom that gains one or more electrons will have a ____________________ charge. An atom that loses one or more electrons will have a ____________________ charge. An atom that gains or loses one or more electrons is called an ____________. A positive ion is called a ______________ and a negative ion is called an _______________. NEGATIVE POSITIVE ION CATION ANION “An-Eye-On” “Cat-Eye-On”

electron shells Atomic number = number of Electrons Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. Electron shells determine how an atom behaves when it encounters other atoms

Electrons are placed in shells according to rules: The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons

Chemical bonds: an attempt to fill electron shells Ionic bonds Covalent bonds

IONIC BOND bond formed between two ions by the transfer of electrons

Ionic Bonds: One Big Greedy Thief Dog!

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

COVALENT BOND bond formed by the sharing of electrons

Covalent Bonds

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

Bohr Model Electron Shells hold a certain number of electrons. The first shell can hold 2 electrons The second shell can hold 8 electrons The third shell can hold 8 electrons The fourth shell can hold 8 electrons The Bohr Model shows the atom and how many electrons in each level.

Bonds Atoms have electrons arranged in energy levels or energy shells Electrons in the last (outermost) shell are called valence electrons Valence electrons let atoms bond with other atoms Ionic bonding Gaining or losing electrons Covalent bonding Sharing electrons

Ionic Bonds and Ions What is an Ion? A charged atom or molecule that has gained or lost an electron Remember, in an ionic bond electrons are lost or gained. Cation : the element that loses an electron Have a positive charge Example: H+1 , Na+ , Ca+2 Anion : the element that gains an electron Have a negative charge Example: S-2 (Sulfide), Cl- (Chloride), OH- (Hydroxide)

Making Compounds from Ions To make a compound from ions, you just switch the superscripts and make them subscripts. Example: Na+ and Cl- would be NaCl and would be called Sodium Chloride. Say the first element normally and add –ide to the end of the second element. Ca+2 and Cl- would be CaCl2 and would be named Calcium Chloride. K+ and S-2 would be K2S and would be named Potassium Sulfide. Mg+2 and Cl- would be what?

Bonds Molecules can bond and “unbond” Atoms can re-arranged in different combinations For example: CaCO3 (1 atom Ca, 1 atom C, 3 atoms O) Add heat to re-arranged the atoms: CaO CO2

Chemical Equations Chemical reactions can be represented by equations CaCO3  CaO + CO2 Reactants Products

Atoms are re-arranged, NOT created or destroyed Law of Conservation of Matter Law of Conservation of Mass

Chemical Changes Matter is conserved  type of atoms does not change Nothing is created or destroyed Mass is conserved  amount of atoms cannot change

Chemical Changes To show conservation of mass  Balance equations Make sure there are the same number of each type of atom in the products and in the reactants

The equation for the burning of methane gas in oxygen is: Balancing Equations The equation for the burning of methane gas in oxygen is: CH4 + 2 O2 → CO2 + 2 H2O Subscript Shows # of atoms Coefficient Shows # of molecules

Balancing Equations 1 C  1 C 4 H  4 H 4 O  4 O No subscript or coefficient is understood to be 1 CH4 + 2 O2 → CO2 + 2 H2O = C1H4 + 2 O2 → C1O2 + 2 H2O1 1 C  1 C 4 H  4 H 4 O  4 O

Practice Balancing 1st Step Mg + 02 MgO Mg- Mg- O- O- 2nd Step How many atoms on each side? Mg + 02 MgO Mg- Mg- O- O- 2nd Step Make same atoms on each side equal by adding a coefficient.

Types of Chemical Reactions Synthesis Reaction 2 or more simple substances combine to form a more complex substance. A+B  AB Decomposition Reaction A more complex substance breaks down into its more simple parts AB  A + B

Types of Chemical Reactions Replacement Reactions Single Replacement One element replaces another element in the compound. AB + C  AC + B Double Replacement Different atoms in two different compounds trade places. AB + CD  AC + BD