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Midterm Review
Chemistry – the study
of matter and the
changes that matter
undergoes
 Element – atoms of only 1 type of atom,
on the periodic table
 Compound – chemical combination of 2
or more elements
 Mixture – physical combination of 2 or
more substances, separated by physical
means
 Physical Properties

Color, melting point, boiling point,
appearance etc.
 Chemical Properties

Burns, explodes, reacts with halogens, etc.
 Accuracy – how close to the right answer
 Precision – how close measurements
are to each other
 Observation – what you see (the crystal
is white)
 Conclusion – what you figure out (the
crystal is NaCl)
Vocab
 Qualitative – description
 Quantitative – numerical measurement
 Metal – Solid at room temp, lustrous
(shiny), conducts electricity
 Nonmetal – may be gas or liquid at room
temperature, nonlustrous, does not
conduct electricity
 Metalloid – some characteristics of both
metals and nonmetals
Measurement
 Always read instruments to 1 digit past
what is marked.
 Final digit is an estimate
Metric conversions to know
 1 km = 1000 m
 1 m = 100 cm
 1 m = 1000 mm
 1 m = 1,000,000 micrometers
 1 cm3 = 1 ml
Dimensional Analysis Example
 Convert 12 km to cm
 12km * 1000m * 100cm = 1,200,000 cm
1 km
1m
Expressed in scientific notation
1.2 x 106 cm
Sig Figs
 0.00043

2
 12000

2
 120.

3
Sig Digs
 12.35 * 2.4 will have how many sig digs?
2 because that is the smaller number of sig
digs.
Numbers
 Scientific Notation – 1 number to the left
of the decimal, * 10 to the appropriate
power. Example 6.02 * 1023
 Numbers greater than 1 have positive
exponents, less than 1 have negative
exponents.
Density
 Density is mass/volume
 Density of water is 1 g/ml or 1g/cm3
 If an object is less dense, then it floats,
more dense it sinks.
 Will an object with a mass of 2.3 grams
in 3 ml sink or float?
 Float (density 0.77 g/ml)
Percent error
(experimental-accepted)

accepted
*100%
 Rutherford – Gold foil experiment,

small, concentrated positively charged
nucleus
 Bohr – Electrons orbit the nucleus
 Quantum Model – Electrons in clouds of
probability around nucleus
Atoms
 Protons have a charge of +1 mass 1
amu
 Electrons have a charge of -1, mass
1/2000 amu.
 Neutrons have no charge, mass of 1
amu
Atoms
 Atomic number = number of protons
 Mass number = protons + neutrons
 Average atomic mass =
sum of mass number *percent for each isotope/100



Example lead is 90% Pb-207 and 10% Pb-209. What
is the average atomic mass for lead?
[(207*90) + (209*10)]/100 =
207.2
Mass number
charge
Symbol
Atomic number
7
+1
Li
3
How many protons, neutrons, electrons?
Atoms
 Protons and neutrons are in the nucleus
and are most of the mass of an atom
 Electrons are in the cloud around the
nucleus
 Protons determine which element an
atom is
 Electrons determine the chemical
properties of an atom
Vocab
 Isotopes – atoms with the same number of
protons but different numbers of neutrons
 Ions – atoms with a charge


Cation – an atom that loses 1 or more electrons
and has a positive charge. Smaller than original
atom.
Anion – an atom that gains 1 or more electrons
and has a negative charge. Larger than the
original atom.
Electrons and Ions
 Valence electrons are the electrons in
the outer shell
 An atom gains or loses electrons until it
has 8 (or 0) in the outer shell
 Lewis Dot Structure
Remember how to find charge
on an ion

+1 +2
+3 - -3 -2 -1 0
Ionic and covalent compounds
 Ionic bonds are formed

Between a metal and a non metal
 Covalent bonds are formed

Between 2 non metals
Naming Compounds – Ionic
Group 1 or 2 metals name of metal, nonmetal
ends in ide




NaF –
sodium fluoride
Na2SO4
– sodium sulfate
 Transition or other metals



Needs Roman numerals
Fe2O3
Iron (III) oxide
Naming Compounds –
Covalent
 Need prefixes



For all but 1 of first element
Always for 2nd element, end in – ide
CO2
 Carbon

dioxide
N2O5
 Dinitrogen
pentoxide
Writing formulas – ionic
compounds
 All ionic compounds are neutral, so

Positive charges = negative charges
 Roman Numeral tells charge of ion

Iron (II) chloride
FeCl2

Aluminum nitrate
Al(NO3)3
LAW OF CONSERVATION
OF MATTER
number and type 
number and type
→ READ as an = sign
 A half life is the time it takes for half of it
to
a. Become stable
b. Undergo fission
c. Decay
d. Undergo oxidation
Nuclear decay, read → as an
equals sign
Complete the following nuclear
 equation:
3919K + →
4 He
2
+ ____
3517Cl (alpha decay)
31H + 21 H → ___ + 10n
42He (fusion reaction)
Moles – do not forget anything
from the test!