UNIT 1: ATOMS, ELEMENTS AND
PERIODICITY
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1 Ionization Energy
The energy defined as the energy required to remove
one mole of electrons, from one mole of gaseous
atoms to produce one mole of gaseous ions.
Related to nuclear charge (how many protons) and
the shielding effect of the inner electrons. Note:
shielding is related to the distance of the electrons
from the nucleus
Variations in ionization energy have to do with ½ full
shells and moving from s to p orbitals
Ionization energies get larger 1st < 2nd < 3rd
Electronegativity
The ability of an atom within a covalent bond, to
attract electrons to itself. Non-metal elements attract
electrons more than metals atoms
Increases across a period and decreases down a group
ATOMIC SIZE
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Size decreases across a period because
nuclear charge increases – no extra
shielding
Size increases down a family – valence
electrons enter new shells, away from the
nucleus
Cations – smaller than atom because they experience
less electron-electron repulsion
Anions – larger than atom because they experience
more electron-electron repulsions
(When comparing go down then across)
Physical Properties Within A Group
As ionization energy decrease, the reactivity increases
EMPIRICAL FORMULA
UNIT 1: ATOMS, ELEMENTS AND
PERIODICITY
Simplest whole number ratio of the atoms
of each element in the compound
GENERAL INFORMATION
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Atomic # = # of protons, # of electrons
Atomic Mass = # of protons + # of neutrons
Rows on Periodic Table – Periods
Columns on Periodic Table – Families (Have same # of valence e-
To calculate from mass data
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PERCENT COMPOSITION
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TO determine the percentage by mass, express the mass of each
element as a percentage of the total mass of the compound
If given the percent composition you can assume 100 grams
% by mass = (mass of element in 1 mole of compound) / (molar mass
of compound) x 100
Mass percent = (mass of solute/mass of solution) x 1--
Assume 100 g sample, the % by
mass
Find AM (from periodic table)
% by mass/AM = # of moles
Divide by the smallest
Determine the Empirical Formula
(Whole number Ratios)
MOLECULAR FORMULA
To find the molecular formula take the
given MW and divide by the Molar Mass of
the Empirical Formula. Multiple each
element in the compound by the result.
Ie. HO (EF) H2O2 (MF)
THE MOLE
ISOTOPES
# of particles in 1 mole = 6.022 x
1023
Isotopes differ ONLY in the number of
neutrons (same # of p+ & e-)
Masses are expressed in amu
Relative atomic mass is defined as the
weighted average of the mass of all
isotopes.
1 mole has a mass = Molar Mass
# of moles = mass given/ Molar
mass
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Used to detect isotopes
Each line represents one isotope (yaxis = % abundance, x-axis = amu)
(% abundance) (MM) + (% abundance)
(MM)
ATOMS & ELECTRONIC CONFIGURATION
3 isotopes
Quantum Numbers
n= principal
l = orbital ( 0 = s, 1=p, 2=d, 3=f)
ml = -l to l
ms = +/- 1/2
(speed of light, wavelength, frequency,)
MASS SPECTROSCOPY
Electron configuration of ion, eliminate
highest principal quantum numbers first
PHOTOELECTRON SPECTROSCOPY
COLOUMBS LAW :
EFFECTIVE NUCLEAR CHARGE: You can increase the
effective nuclear charge by adding protons, or
decreasing electrons. The effective nuclear charge is
the pull of the electrons towards the nucleus.
ELECTRON REPULSION: add electrons, increase
repulsion
Ionization Energies
Look for large jumps between the different ionization energies to determine the
number of valence electrons
1 valence
electron
Paramagnetic- unpaired electrons
Diamagnetic – paired electrons
Isoelectronic Species – Elements that have same electronic configuration