Unit 2 Part 2: Periodic Trends - SSI Chemistry...Periodic Trends: Atomic Radius The atomic radius decreases across a period. This is because of an increasing positive charge in the

Unit 2 Part 2: Periodic Trends

Outline

Classification of elements using properties

Representative elements, transition elements

Metals, nonmetals and metalloids

Classification of elements using electron configuration

Valence electrons and period

s, p, d, f blocks

Periodic Trends

Atomic radius, ionic radius

Ionization energy

Electronegativity

Classifying the Periodic Table: Using Physical and Chemical Properties

Representative elements: groups 1-2 and 13-18

Transition elements: groups 3-12

Elements are classified as metals, metalloids or nonmetals.

Metals:

Shiny

Good conductors of electricity and heat

Malleable: can be shaped into many shapes

Ductile: can be drawn into wires


Special metals:

Group 1 elements are called alkali metals. They are very reactive.Eg.

Group 2 elements are called alkaline earth metals.They are also very reactive.Eg.


Transition metals:

Transition metals: Groups 3-12

Inner transition metals: lanthanide series and actinide series.


Nonmetals:

Gas, solid, or liquid.

Brittle

Poor conductors of heat and electricity

Eg. Group 17: Halogens

Eg. Group 18: Noble gases



Metalloids:

Properties of both metals and non metals

Eg. Silicon, Si:


Classifying the Periodic Table Using Electron Configuration Electron configuration determines the chemical

properties of an element.

Valence electrons are electrons in the highest principal energy level of an atom.

Atoms in the same group have similar chemical properties because they have the same number of valence electrons.

Eg. Group 1

Each of the representative groups (column in groups 1,2 and 13 to 18) has its own valence electron configuration.

Valence electrons and period:

The principal energy level of an element’s valence electrons = the period of the periodic table that the element is in. Eg.

Classifying the Periodic Table Using Electron Configuration

s-block, p-block, d-block, and f-block elements

The periodic table has columns and rows of varying sizes.

This is because the table has been divided into sections, or blocks, representing the valence electrons’ sublevels. (ie. s, p, d, or f)


1. Which groups are the s-block elements? What do the valence electrons for these groups look like? Why are there only two groups in the s-block?

2. Which groups are the p-block elements? Why are there no p-block elements in period 1? Why are there six groups in the p-block?

3. What is a characteristic of the d-block? Example: Why are there ten groups in the d-block?

4. Which groups make up the f-block elements? Why are there 14 groups in the f-block?


Periodic Trends: Atomic RadiusMany properties change in a predictable way.

This pattern is called a trend.

An atom’s radius is defined by how close it can get to another atom.

This is because an atom has no clearly defined edge.

Periodic Trends: Atomic Radius A metal atom’s radius is defined as half the distance

between neighboring nuclei in a crystal structure.

A nonmetal’s atomic radius is defined as half the distance between nuclei of identical atoms that are bonded together.

Periodic Trends: Atomic Radius The atomic radius decreases across a period.

This is because of an increasing positive charge in the nucleus, and also because the principal energy level within a period remains the same.

No additional electrons come between the valence electrons and the nucleus.

Periodic Trends: Atomic RadiusThe atomic radius increases down a group.Electrons are added to

orbitals in higher principal energy levels =further from the nucleus.

The orbitals between the nucleus and the outer electrons shieldthe outer electrons from the nucleus.

P. 189 Q16-19

Periodic Trends: Atomic Radius

Atoms can gain or lose electrons to form a charged version of itself, which is called an ion.

When atoms lose electrons, they form _______________ ions called cations.

When atoms gaim electrons, they from _______________ ions called anions.

Periodic Trends: Ionic Radius

Atoms can gain or lose electrons to acquire a full set of eight valence electrons.

This is called the octet rule.This is because the electron configuration of

filled s and p orbitals of the same energy level is very stable.

Exception: period 1 elements. They are complete with only two valence electrons.


Positively charged ions:

Smaller than the “parent” atom.

Because:

1. The lost electron is a valence electron (in the outer shell) so the ion’s radius is smaller than before.

2. Less electrostatic repulsion because there are fewer electrons. So the remaining electrons experience a greater pull to the positively charged nucleus.


Negatively charged ions:

Larger than the “parent” atom.

Because:

More electrostatic repulsion because there are more electrons, which forces them to move further apart. The increased distance between the outer electrons results in a larger radius.



Periodic Trends: Ionic Radius Across a period:

Ionic radius decreases.

Down a group: Ionic radius increases(electrons are in higher principal energy levels = bigger radius)

Periodic Trends: Ionization Energy

Energy required to remove an electron from a gaseous atom.

First ionization energy:

Second ionization energy:

High ionization energy means _________

Low ionization energy means __________



Across a period: ionization energies usually increase.

Down a group: ionization energies usually decrease.

Jump in ionization energies after all the valence electrons are removed.

Periodic Trends: Electronegativity

The ability of an atom to attract electrons in a chemical bond.

Periodic Trends: Electronegativity

Across a period: increases

Down a group: decreases

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Unit 2 Part 2: Periodic Trends - SSI Chemistry...Periodic Trends: Atomic Radius The atomic radius decreases across a period. This is because of an increasing positive charge in the