Atoms and Elements
Atoms = basic unit of matter
Protons
 Positively charged subatomic particles
 Located in the nucleus of an atom
 Make up most of the atom’s mass
 Pos. charge of proton = Neg charge of electron
(e-)
 1 proton has as much mass as around 1840 e-‘s
 Periodic table is arranged in increasing number
of protons
Neutrons
 Neutral subatomic particle
 Located in the nucleus of the atom
 DOES contribute to the mass of the atom
 Most common type of hydrogen (called
protium) contains NO neutrons. However,
deuterium (heavy hydrogen) does contain 1
proton and 1 neutron in the nucleus.
Electrons
 Negatively charged subatomic particle
 Located in the space outside of the nucleus
 Mass of the electron is negligible
Subatomic Particles Summary
Subatomic
Mass in grams
Particle
Electron (e-)
9.11 x 10-28 g
Proton (p, +)
1.67 x 10-24g
Neutron (n,o)
1.67 x 10-24 g
Mass in amu
0.000549 amu
1.0073 amu
1.0087 amu
Distinguishing between Atoms
Atomic Number
 Is the number of protons in the nucleus of an atom
of an element
 Used to identify an element
 ALWAYS a whole number
Mass Number
 Most of the atom’s mass is concentrated in the
nucleus (protons and neutrons)
 Mass Number = # of protons + # of neutrons
 Electron mass is so small that it is NOT included
in the mass #
 Number of neutrons = Mass # - Atomic #
Isotopes
 All atoms of the same element have the same # of
protons but may have DIFFERENT number of
neutrons
 Isotope  atoms of the same element with different
# of neutrons
 Often identify an element by mass number
 Example: carbon-12, carbon-14
Atomic Mass
 Atomic masses shown on the PT (periodic table)
represent a weighted average based on the relative
abundance of each isotope of a particular atom.
 Atomic mass unit (amu) is a unit of mass equal to
1/12th the mass of a carbon-12 atom.
 amu’s are used instead of grams because the
masses of subatomic particles are small
 More useful to compare the relative masses of
atoms using a reference isotope as a standard
 Carbon-12 was chosen as the reference isotope.
Average Atomic Mass
The atomic mass on the periodic table is an average of
all the isotopes of that particular element. Every
element (except the synthetic ones) has one or more
isotopes
Σ (mass of isotope X relative abundance)
Practice:
1. Neon has two isotopes: Ne-20 (having a mass of 20
u) and Ne-22 (having a mass of 22 u). Given the
following abundances of these isotopes in nature,
what is the average atomic mass of neon?
Mass number
Abundance
Ne-20
90%
Ne-22
10%
2. What is the average atomic mass of hafnium given
the following abundance information on its
isotopes?
Mass number
Abundance
Hf-176
5%
Hf-177
19 %
Hf-178
27 %
Hf-179
14%
Hf-180
35%
Ions
General
 Atoms are electrically neutral--- can either gain or
lose e-‘s to become charged
 Ion  charged atom
Cations
 Positively charged atom because it has lost 1 or
more e-‘s
o Na – 1e- = Na+
o Ca – 2e- = Ca2+
o Al – 3e- = Al3+
Anions
 Negatively charged atom because it has gained 1
or more e-‘s
o Cl + e- = Clo S + 2e- = S2-
Matter = the “stuff” that makes up the entire universe.
EVERYTHING!
 Two characteristic
o It has mass
o Occupies space
Elements or Atoms = substances that cannot be broken
down into other substances by chemical means
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The periodic table!
Magnesium
Calcium
Hydrogen
Compounds = substances that are made up of elements
and therefore can be broken down into parts
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Compounds →Elements
Water
Gasoline
Ethanol (Rubbing alcohol)
CO2
Mixtures:
 Something that has other things in it: physical blend
of two or more components
 Can be broken down into compounds and/or elements
Two Types of Mixtures
 Heterogeneous – Pancake Batter, chicken noodle
soup
 Homogeneous – Olive Oil
o Also called Solutions
Solutions
 Made by combining a solute (less) and a solvent
(more)
 Composition may vary
 Can be any state of matter (solid, liquid, or gas)
 Examples—window glass, metal alloys, air, brine
solution
Separating Mixtures—
 Filtration = separates a solid and a liquid in a
heterogeneous mixture
o Gravity filtration – use filter paper and a funnel
o Vacuum filtration
Distillation = separates dissolved solids from a liquid,
which is boiled to produce a vapor that is then condensed
into a liquid
o Distillation columns
Suspensions
 A combination of two or more substances that never
dissolve and will settle out by size over time
o Oil and Water
Bonding and CHNOPS
Ionic Bonds - bonds formed by the transfer of electrons
 Formed between ions = Na+ and Cl- = NaCl
Covalent Bonds – bonds formed by sharing electrons
 CO2 – both C and O have eight electrons in the outer
shell
ANIMATIONS!
van der Waals Forces – slight attraction between an
oppositely charged “cloud” of two nearby molecules.
 Not as strong as ionic and covalent, but will hold
molecules together.
 London-London Dispersion – weakest of the three,
happens when there is a temporary charge
development that occurs spontaneously in all
elements and compounds, even neutral ones
 Dipole-Dipole – next strongest and it happens when
you have a compound with a permanent partial
positive and negative charges
 Hydrogen bonds – strongest form of van der Waals,
a VERY strong dipole-dipole that happens when
hydrogen bonds to highly electronegative elements
(fluorine, nitrogen, and oxygen).
CHNOPS
Biological compounds within the universe
 C-Carbon
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H-Hydrogen
N-Nitrogen
O-Oxygen
P-Phosphorous
S-Sulfur
Responsible for building carbohydrates, proteins,
lipids, and nucleic acids