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Molecules and Chemical Formulas
• Atoms bind to other atoms to form molecules• Ionic Bonding: Giving and taking electrons (Metal-
nonmetal bond)• Covalent Bonding: Sharing electrons (nonmetal-
nonmetal bond)• There are gasses that are bound to themselves as
elements:Hydrogen = H2 Nitrogen = N2 Oxygen = O2
Fluorine = F2 Chlorine = Cl2 Bromine = Br2
Iodine = I2
You need to memorize these!
Formulas
• We can represent molecules with molecular and empirical formulas.• Molecular Formula = shows actual number of
atoms in a molecule.
• Empirical Formula = shows ratio of atoms in a molecule.
22OH
HOOCH2
TRY IT OUT!
1. Determine the empirical formula of the following compound: B2H6
2. Is this a molecular or empirical formula: N4O6?
Ions and Ionic Compounds
• Recall, an ion forms when an atom gains or loses electrons• Elements/compounds will gain or lose electrons in
order to achieve a full outer valence shell.• Cation – A positively charged ion that forms when
electrons are lost• Anion – A negatively charged ion that forms when electrons are gained.
Cl Cl-
Na Na+
Gains 1 electron, so it ends with a
negative 1 charge
IONIC ATTRACTION
• Just like opposite poles of a magnet attract, oppositely charged ions attract.• Here, our positively charged
Sodium Ion and negatively charged Chlorine Ion are attracted.• They remain ions, but stick
together in a lattice (3D grid pattern) as other ions join them.
Cl- Na+
Cl- Na+
Cl-Na+
Na+
Cl-
Determining Ionic Formulas
• To determine the ionic formula that forms between two ions you need to do a few steps before beginning:1. Make sure you have both a metal and non-
metal. This indicates that an ionic bond will form
2. If a polyatomic ion is present, then make sure to put parentheses around it before beginning
CLASS EXAMPLE
Determine the formula when the following join in an ionic bond:1. Sodium and oxygen2. Potassium and phosphate