Chemistry

Question 1

Proton

Answer 1

Carries a single positive electric charge; multiple protons repel each other

The number of protons of an atom determines its identity (atomic number)

Question 2

Neutron

Answer 2

Carries no electric charge; helps hold the nucleus of an atom together against the repelling electric force of protons

Usually about equal distribution to number of protons; larger atoms generally have more neutrons than protons

Question 3

Electron

Answer 3

Carries a single negative electric charge

Electrically neutral atoms have equal numbers of protons and electrons

Much smaller than protons and neutrons (1/1800th the mass)

Question 4

Atomic mass

Answer 4

Defined by the total number of neutrons and protons (electrons are too small to contribute notably to atomic mass)

Atomic mass units (amu)
- protons and neutrons have atomic mass of approximately 1 amu

Question 5

Isotope

Answer 5

Atoms with the same number of protons but different numbers of neutrons

Eg.,
Au has one stable isotope
- 79 protons, 118 neutrons - 197 amu
Cu has two stable isotopes
- Cu-63 (29 protons, 34 neutrons - 63 amu)
- Cu-65 (29 protons, 36 neutrons - 65 amu)

Isotopes don’t usually affect the chemistry of materials

Question 6

Ionic/atomic charge

Answer 6

Denoted by the sum of charges (protons, neutrons, and electrons)

An atom is neutral in a basic atom of a given element with all its allotted electrons
Ie, all negative charges (of electrons) are balanced by all positive charges (of protons)

Question 7

Valence state/charge

Answer 7

The resulting charge of an atom prone to gaining or losing electrons from outside sources

Question 8

Ion

Answer 8

Charged atom

Occurs when atom gains or loses electron(s)

Exchange of electrons almost always occurs within outermost portion of electron cloud

Question 9

Cation

Answer 9

Positively charged ion

Question 10

Anion

Answer 10

Negatively charged ion

Question 11

Ionic radius

Answer 11

Distance from the centre of the nucleus to the limit of the electron cloud of an ion

Measured in Ångstroms (Å)
- 1 Å = 1/10 of a nanometre (.000000001, or 10-9, metre)

Question 12

Elements

Answer 12

The basic building blocks of matter; composed of identical atoms

~117 known elements
~90 are naturally occuring, usually combined with other elements in compounds; others are synthetic

Question 13

Relationship between atoms, elements, compounds, and mixtures

Answer 13

Elements = composed of identical atoms

Compounds = 2+ elements joined together through chemical bonds

Mixtures = 2+ compounds that are not interacting through chemical bonding (interlocking physical network of mineral grains)

Question 14

Ionic bonding

Answer 14

One atom with a strong tendency to gain electrons (anion-)
+
One atom with a strong tendency to lose electrons (cation+)
=
The cation donates electrons and becomes positively charged, while the anion becomes negatively charged with an extra electron

Most mineral bonds tend to be more ionic (but it is a spectrum)

Question 15

Valence electron

Answer 15

Electron in the outer shell of an atom (lost or gained; causes changes to the valence state of the atom)

Question 16

Covalent bonding

Answer 16

Atoms share valence electrons between them

Organic compounds tend to be more covalent (C-C)
Observed in diamonds

Question 17

Metallic bonding

Answer 17

Valence electrons are shared throughout the entire material, not simply between two atoms, and are free to move about

Typical in metals, and the reason metals are so good at conducting electricity

Question 18

Most abundant elements

Answer 18

98.5% of earth’s crust:
oxygen (46%)
silicon (27.5%)
aluminum (8%)
iron (5%)
calcium (4%)
sodium (3%)
potassium (3%)
magnesium (2%)

Question 19

Native elements

Answer 19

Elements that occur by themselves in rock (not chemically bonded to other elements)

20 elements can occur as solids in their native state
eg., Au, Ag, Cu, Pt

Question 20

Base metals

Answer 20

Metals that react (corrode) when exposed to oxygen to form metal oxide

Normally found as oxide or sulfide minerals in nature, but can be present as native metals

Eg., Fe and Cu

Question 21

Noble metals

Answer 21

Metals that do not react to oxygen

Historically, the term precious metal refers to noble metals, but others can be included (eg., U)

Eg., Au and Pt

Question 22

Precious metals

Answer 22

Valueable metals
- noble metals
- uranium (U) - neither native nor noble, but valuable

Question 23

Native metals

Answer 23

Characterized by metallic bonds
Au, Ag, Cu, Pt

Traits:
good electrical conductivity
good thermal conductivity
high density
malleability
ductility
metallic luster

Question 24

Measuring mass of precious metals
SI & Imperial

Answer 24

System Internationale (SI)
1 gram = mass of 1 cm3 of water (at 0°C and 1 atm) *original def., approx/variable - now we use constants
1 gram = 1 mL (approx)
1000mg = 1 g; 1000g = 1kg

Imperial system
1 oz = 28 g
16 oz = 1 lb
1 troy oz = ~31.1 g
12 troy oz = 1 lb

Question 25

Measuring purity of precious metals

Answer 25

Karats /24
14K = 58% (14 parts gold, 10 parts something else)
18K = 75% pure
22K = 92% pure
24K = 100% pure

Fineness (silver)
value of 1 = 100% pure
(.)999 = 99.9% pure
935 = 93.5% pure

Platinum group metals
scale of 1-1000
900 = 90% pure

Question 26

Sterling silver

Answer 26

standard alloy
92.5% Ag and 7.5% Cu

Question 27

Weighing gemstones

Answer 27

Carat