Unit 2 – Matter and Chemical Change TOPIC 6

TOPIC 6 – CHEMICAL COMPOUNDS Compounds are formed when elements combine together. They are held together by chemical bonds which form when electrons are shared or exchanged. There are 2 kinds of compounds: Ionic compounds – e - s transferred Molecular compounds – e - s shared

UNDERSTANDING FORMULAS A chemical formula uses symbols and numbers for a pure substance. Eg. Water H2OH2O Symbol for Hydrogen # of hydrogen atoms Symbol for Oxygen No number means 1 atom of oxygen

MOLECULAR COMPOUNDS A molecule is the smallest unit of a pure substance, a cluster of atoms together. Diatomic molecules have 2 of the same element together. Eg. H 2 N 2 O 2 Attraction between molecules is weak

NAMING MOLECULAR COMPOUNDS 1.Write the name of the first element 2.Change the ending on the name for the second element to ______ide. 3.Use prefixes to indicate the number of each type of atom in the formula.

PREFIXES mono- 1 hepta- 7 di- 2 octa- 8 tri- 3 nona- 9 tetra- 4 deca- 10 penta- 5 hexa- 6 we don’t put mono on the first element!

EXAMPLES #1- FORMULAS TO NAMES CCl 4 carbonmonotetra I’m a Binary Compound 2. Write number of atoms 1. Write names of elements Final Name chlor ine ide If first prefix is mono, it is implied and not written

EXAMPLES #2- FORMULAS TO NAMES N2S5N2S5 nitrogen di penta I’m a Binary Compound 2. Write number of atoms 1. Write names of elements Final Name sulf ur ide

EXAMPLE #1- NAMES TO FORMULAS Sulfur trioxide S O 1 3 I’m a Binary Compound 2. Write number of atoms 1. Write symbols of elements Final Formula If no prefix, then 1 is implied and not written

EXAMPLE #2 - NAMES TO FORMULAS dichlorine heptaoxide Cl O 2 7 I’m a Binary Compound 2. Write number of atoms 1. Write symbols of elements Final Formula

EXAMPLE #3- NAMES TO FORMULAS dinitrogen tetraoxide N O 2 4 I’m a Binary Compound 2. Write number of atoms 1. Write symbols of elements Final Formula

IONIC COMPOUNDS When an atom gains or loses an electron it becomes an ion. Ionic compounds form when electrons are transferred from a metal to a nonmetal. Attraction between ions is strong Naming ionic compounds is just like molecular compounds except you don’t use prefixes.

The formation of ions Ions form to fill their energy levels Ions are atoms that have gained or lost electrons.

NAMING MONATOMIC IONS Cations : name of element followed by ion Anions : element suffix ___ide followed by ion Metals form cations Electrons less than protons Nonmetals form anions Electrons greater than protons

BELL WORK When an atom loses or gains an electron, it is called an __________. When an atom has less electrons than protons it’s called a ______________. Ionic compounds are formed between two kinds of elements, what are they? What is the chemical name of PCl 5 ? Draw the Lewis dot diagram for methane (CH 4 ).

IONIC AND MOLECULAR COMPOUNDS Ionic compounds form when metal atoms are attracted to nonmetal atoms.

By Ken Costello

+ _ battery compass Coil of wire + _ What’s an ion? Let’s find out…

+ _ battery compass Coil of wire Copper Chloride + _ Switch is open. Nothing happening yet.

+ _ battery compass Coil of wire Copper Chloride If copper atoms are going to the negative side, what charge do they have? What about the chlorine atoms? + _

+ _ battery compass Coil of wire Copper Chloride Since the atoms wandered towards each side, let’s call them IONS from the Greek word, ion, meaning wanderer. + _

+ _ Copper Chloride CuCl Also, since the positive side of a battery is called the anode (way up), we’ll call ions that go towards it anions Since the negative side of a battery is called the cathode (way down), we’ll call ions that go towards it cations. anode cathode + _

IIA IIIAVIAVAIVA Naming compounds by taking a metal from groups 1A, 1B, or 1C, and combining with a non-metal.

Understanding how ions react to other elements will help in naming compounds or coming up with formulas for the compounds.

Types of Crystals Ionic Crystals Lattice points occupied by cations and anions Held together by electrostatic attraction Hard, brittle, high melting point Poor conductor of heat and electricity CsClZnSCaF

Ionic compounds contain oppositely charged particles held together by extremely strong electrostatic inter- actions. The ionic formula is the ratio of positive ions to negative ions E.g. CaCl 2 1 calcium ion : 2 chloride ions