chem: ch 2

atoms, elements, and compounds

relative mass of electron

1/1840

group

vertical, the number of valence electrons

period

horizontal, the number of electron shells in an atom

atomic number (proton number)

number of protons

mass number (relative atomic mass, nucleon number)

number of protons + neutrons

group 8

also known as noble gases, and exist as monoatomic elements

isotopes

atoms of the same elements with the same number of protons/electrons but different number of neutrons

element

pure substance that can’t be broken down by chemical processes, contains one type of atom

compound

pure substance containing 2+ elements that are chemically combined, can be molecules/ionic compound

mixture

made up of 2+ substances that aren’t chemically combined

group 1 (ionic structure)

lose 1 electron = 1+

group 2 (ionic structure)

lose 2 electrons = 2+

group 3 (ionic structure)

lose 3 electrons = 3+

group 5 (ionic structure)

gain 3 electrons = 3-

group 6 (ionic structure)

gain 2 electrons = 2-

group 7 (ionic structure)

gain 1 electron = 1-

cation (positive ion)

forms when an atom has lost electrons, has more protons than electrons

anion (negative ion)

forms when an atom has gained electrons, has more electrons than protons

ionic bond

the electrostatic attraction between positive and negative ions, occurring between metal and non-metal atoms

giant ionic lattice

a lattice of alternating positive and negative ions held by ionic bond

covalent bond

a bond formed by sharing electrons between 2 atoms, occurring between 2 non-metal atoms

group 5 (covalent structure)

share 3 electrons

group 6 (covalent structure)

share 2 electrons

group 7 (covalent structure)

share 1 electron

physical properties of simple molecules

1. low melting/boiling point

2. poor conductor of electricity

low melting/boiling point in simple molecules

this is due to weak intermolecular forces between molecules

poor conductor of electricity in simple molecules

this is due to lack of delocalised electrons to conduct electricity

giant covalent structure (macromolecule)

diamond and graphite

structure of diamond

electrical conductivity of diamond

melting point of diamond

hardness of diamond

structure of graphite