periodic trends and electron configurations

UNIT 3

PERIODIC TRENDS and ELECTRON

CONFIGURATIONS

Periodic Table TrendsPeriodic Table Trends

Periodic LawPeriodic Law““When arranged by increasing atomic number, the chemical When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and elements display a regular and repeating pattern of chemical and physical properties.”physical properties.”Atoms with similar properties appear in groups or families (vertical Atoms with similar properties appear in groups or families (vertical columns) on the periodic table.columns) on the periodic table.

all have the same number of valence (outer shell) electrons, which all have the same number of valence (outer shell) electrons, which governs their chemical behavior.governs their chemical behavior.

Atomic RadiusAtomic RadiusRadius is the distance from the center of the Radius is the distance from the center of the nucleus to the nucleus to the ““edgeedge”” of the electron cloud. of the electron cloud.

Since a cloudSince a cloud’’s edge is difficult to define, s edge is difficult to define, scientists use covalent radius, or half the scientists use covalent radius, or half the distance between the nuclei of 2 bonded distance between the nuclei of 2 bonded atoms.atoms.Atomic radii are usually measured in Atomic radii are usually measured in picometers (pm) or angstroms (Å). An picometers (pm) or angstroms (Å). An angstrom is 1 x 10angstrom is 1 x 10-10-10 m. m.

Ex. Two Br atoms bonded together are 2.86 Ex. Two Br atoms bonded together are 2.86 angstroms angstroms

apart. So, the radius of each apart. So, the radius of each atom is 1.43 Å.atom is 1.43 Å. 2.86 Å

1.43 Å 1.43 Å

The trend for atomic radius The trend for atomic radius smaller at the top to larger at the bottom.smaller at the top to larger at the bottom.add an entirely new energy level to the electron cloud, making the add an entirely new energy level to the electron cloud, making the atoms larger with each step.atoms larger with each step.

The trend across a horizontal period is less obvious.The trend across a horizontal period is less obvious.Each step from left to right adds a proton and an electron (and 1 or 2 Each step from left to right adds a proton and an electron (and 1 or 2 neutrons) and electrons are added to existing energy levels.neutrons) and electrons are added to existing energy levels.

The effect is that the more positive nucleus has a greater pull on the The effect is that the more positive nucleus has a greater pull on the electron cloud.electron cloud.The nucleus is more positive and the electron cloud is more negative.The nucleus is more positive and the electron cloud is more negative.The The increased attraction pulls the cloud inincreased attraction pulls the cloud in, making atoms smaller as we , making atoms smaller as we move from left to right across a period.move from left to right across a period.

Ionization EnergyIonization EnergyIf an electron is given enough energy to overcome the forces If an electron is given enough energy to overcome the forces holding it in the cloud, it can leave the atom completely.holding it in the cloud, it can leave the atom completely.

The atom has been The atom has been ““ionizedionized”” or charged. The number of protons or charged. The number of protons and electrons is no longer equal.and electrons is no longer equal.The energy required to remove an electron from an atom is The energy required to remove an electron from an atom is ionization energy. (measured in kilojoules, kJ)ionization energy. (measured in kilojoules, kJ)

The larger the atom is, the easier its electrons are to remove.The larger the atom is, the easier its electrons are to remove.Ionization energy and atomic radius are inversely proportional.Ionization energy and atomic radius are inversely proportional.

Electron AffinityElectron AffinityElectron affinity is the energy Electron affinity is the energy changechange that occurs when an atom that occurs when an atom gains an electrongains an electron (also measured in kJ). (how well atoms attract (also measured in kJ). (how well atoms attract electrons)electrons)

Electron affinity is usually exothermic, but Electron affinity is usually exothermic, but not alwaysnot always..

Electron affinity is exothermic if there is an empty Electron affinity is exothermic if there is an empty or partially empty orbital for an electron to or partially empty orbital for an electron to occupy.occupy.If there are no empty spaces, a new orbital or If there are no empty spaces, a new orbital or energy level must be created, making the process energy level must be created, making the process endothermic.endothermic.

Metals: Metals like to lose valence electrons to form cations to have Metals: Metals like to lose valence electrons to form cations to have a fully stable octet. They absorb energy to lose electrons. The a fully stable octet. They absorb energy to lose electrons. The electron affinity of metals is lower than that of nonmetals.electron affinity of metals is lower than that of nonmetals.Nonmetals: Nonmetals like to gain electrons to form anions to have Nonmetals: Nonmetals like to gain electrons to form anions to have a fully stable octet. They release energy to gain electrons to form an a fully stable octet. They release energy to gain electrons to form an anion; thus, electron affinity of nonmetals is higher than that of anion; thus, electron affinity of nonmetals is higher than that of metals.metals.

ElectronegativityElectronegativityElectronegativity is a measure of an atomElectronegativity is a measure of an atom’’s attraction for another s attraction for another atomatom’’s electrons.s electrons.

It is an arbitrary scale that ranges from 0 to 4.It is an arbitrary scale that ranges from 0 to 4.The units of electronegativity are Paulings.The units of electronegativity are Paulings.Generally, metals are electron givers and have low Generally, metals are electron givers and have low electronegativities.electronegativities.Nonmetals are are electron takers and have high Nonmetals are are electron takers and have high electronegativities. electronegativities. What about the noble gases?What about the noble gases?

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Periodic Trends Rap

Electron ConfigurationElectron ConfigurationQuantum Mechanical Model (electron cloud)Quantum Mechanical Model (electron cloud)

Energy is quantized. It comes in chunks.Energy is quantized. It comes in chunks.A quanta is the amount of energy needed to A quanta is the amount of energy needed to move from one energy level to another.move from one energy level to another.Since the energy of an atom is never Since the energy of an atom is never ““in betweein betweenn ”” there must be a quantum leap in energy. there must be a quantum leap in energy.Schrödinger derived an equation that described Schrödinger derived an equation that described the energy and position of the electrons in an the energy and position of the electrons in an atomatom

Atomic OrbitalsAtomic OrbitalsWithin each energy level the Within each energy level the complex math of Schrödinger's complex math of Schrödinger's equation describes several shapes.equation describes several shapes.These are called atomic orbitalsThese are called atomic orbitals

Regions where there is a high Regions where there is a high probability of finding an electronprobability of finding an electron

S orbitalsS orbitals• 1 s orbital in1 s orbital inevery energy levelevery energy level

1s 2s1s 2s 3s 3s• Spherical shapedSpherical shaped• Each s orbital can hold 2 electronsEach s orbital can hold 2 electrons• Called the 1s, 2s, 3s, etc.. orbitalsCalled the 1s, 2s, 3s, etc.. orbitals

P orbitalsP orbitals• Start at the second Start at the second

energy level energy level • 3 different directions3 different directions• 3 different shapes3 different shapes• Each orbital can hold Each orbital can hold

2 electrons2 electrons• The p Sublevel has 3 The p Sublevel has 3

p orbitalsp orbitals• Called the 2p, 3p, Called the 2p, 3p,

etc.etc.

D orbitalsD orbitals• The D sublevel starts in the 3The D sublevel starts in the 3rdrd energy energy

level level • 5 different shapes (orbitals)5 different shapes (orbitals)• Each orbital can hold 2 electronsEach orbital can hold 2 electrons• The D sublevel has 5 D orbitalsThe D sublevel has 5 D orbitals• Called the 3d, 4d, etc.Called the 3d, 4d, etc.

F orbitalsF orbitals• The F sublevel starts in the fourth The F sublevel starts in the fourth

energy levelenergy level• The F sublevel has seven different The F sublevel has seven different

shapes (orbitals)shapes (orbitals)• 2 electrons per orbital2 electrons per orbital• The F sublevel has 7 F orbitalsThe F sublevel has 7 F orbitals• ONLY 4F and 5FONLY 4F and 5F

SummarySummary

s

p

d

f

# of shapes (orbitals)

Max # of electrons

1 2 1

3 6 2

5 10 3

7 14 4

SublevelStarts at energy level

Atomic OrbitalsAtomic Orbitals

• The periodic table gives clues to how The periodic table gives clues to how electrons fill each energy level (shell)electrons fill each energy level (shell)

• Principal Quantum Number (n) = the Principal Quantum Number (n) = the energy level of the electron. (same as the energy level of the electron. (same as the period it’s in)period it’s in)

• Three ways to represent where Three ways to represent where electrons areelectrons are

• Electron ConfigurationElectron Configuration

• Noble Gas ConfigurationNoble Gas Configuration

• Orbital NotationOrbital Notation

Orbital Filling Orbital Filling Rules!!!!Rules!!!!

• Aufbau principleAufbau principle- electrons enter the - electrons enter the lowest energy first.lowest energy first.– This causes difficulties because of the This causes difficulties because of the

overlap of orbitals of different energies.overlap of orbitals of different energies.

• Pauli Exclusion PrinciplePauli Exclusion Principle- at most 2 - at most 2 electrons per orbital - different spinselectrons per orbital - different spins

• HundHund’’s Rules Rule- When electrons occupy - When electrons occupy orbitals of equal energy they donorbitals of equal energy they don’’t pair t pair up until they have to .up until they have to .