Chemistry Flashcards
Proton
Carries a single positive electric charge; multiple protons repel each other
The number of protons of an atom determines its identity (atomic number)
Neutron
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
Electron
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)
Atomic mass
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
Isotope
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
Ionic/atomic charge
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)
Valence state/charge
The resulting charge of an atom prone to gaining or losing electrons from outside sources
Ion
Charged atom
Occurs when atom gains or loses electron(s)
Exchange of electrons almost always occurs within outermost portion of electron cloud
Cation
Positively charged ion
Anion
Negatively charged ion
Ionic radius
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)
Elements
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
Relationship between atoms, elements, compounds, and mixtures
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)
Ionic bonding
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)
Valence electron
Electron in the outer shell of an atom (lost or gained; causes changes to the valence state of the atom)
Covalent bonding
Atoms share valence electrons between them
Organic compounds tend to be more covalent (C-C)
Observed in diamonds
Metallic bonding
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
Most abundant elements
98.5% of earth’s crust:
oxygen (46%)
silicon (27.5%)
aluminum (8%)
iron (5%)
calcium (4%)
sodium (3%)
potassium (3%)
magnesium (2%)
Native elements
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
Base metals
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
Noble metals
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
Precious metals
Valueable metals
- noble metals
- uranium (U) - neither native nor noble, but valuable
Native metals
Characterized by metallic bonds
Au, Ag, Cu, Pt
Traits:
good electrical conductivity
good thermal conductivity
high density
malleability
ductility
metallic luster
Measuring mass of precious metals
SI & Imperial
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
Measuring purity of precious metals
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
Sterling silver
standard alloy
92.5% Ag and 7.5% Cu
Weighing gemstones
Carat
