CHM 1011 L2 Periodic Properties

What is periodicity, and what is the modern basis of the periodic table?

Periodicity is the repeating pattern of element properties with increasing atomic number. The modern periodic table is organized by atomic number, or number of protons.

How is effective nuclear charge calculated?

Zeff = Z - S

Z - atomic number

S - screening constant, number of inner electrons

What are the trends in effective nuclear charge?

Increases from left to right, increases down a group

What are the two definitions of atomic radius?

Van der Waals radius: half the shortest distance between nuclei of two nonbonded atoms

Bonding radius: half the internuclear distance between two bonded atoms

What are the periodic trends in atomic radius?

Decreases across a period, increases down a group

Why are cations smaller and anions larger than their parent atoms?

Cations: lose electrons, reducing electron–electron repulsion and sometimes losing an entire energy level

Anions: gain electrons, increasing electron–electron repulsion

What is an isoelectronic series, and how does size change within one?

O, F, Na, Mg, Al.

The size changes because even though the number of electrons are the same, the number of protons is different. The more protons, the bigger the atom would be, because it attracts electrons.

Ionization Energy

The minimum energy required to remove an electron from an atom or ion in its ground state.

What are the general trends in first ionization energy?

Increases across a period, decreases down a group

Why is oxygen’s first ionization energy lower than nitrogen’s?

Nitrogen has a stable, half filled level, oxygen has one parked set of 2p electrons. The repulsion between paired electrons makes one oxygen easier to remove.

Electron affinity

The energy change when an electron is added to a gaseous atom, opposite of ionization.

General trend in electron affinity

Not much change in a group, increases across a period.

Some electron arrangements and especially stable:

• Group 2A (s sublevel is full)

• Group 5A ( p sublevel is full)

• Group 8A ( p sublevel is full)

Physical properties of a metal

Shiny, good conductors of heat and electricity, usually solids, low in ionization energy

Physical properties of nonmetals

May be solid, liquids, gases

Chemical behaviours of metals

They tend to form cations, compounds are metalic, ionic with non-metals.

Chemical behaviours of non-metals

Compounds made only of non-metals are usually molecular

Alkali metals are:

Soft, metallic, found in compounds in nature, not elemental forms, low densities, melting points, ionization energies.

The reactions H2O with alkali metals are:

Exothermic

How do alkaline earth metals compare with alkali?

Higher densities, melting points, ionization energies.

Alkaline earth metals relations with H2O

Be doesn’t react with water, Mg reacts with steam, reactivity increases down the group

Name the state of each element from the Oxygen (Group 6A)

• Oxygen, sulfur, selenium: nonmetals

• Tellurium: metalloid

• Polonium: metal