Periodic Trends

Dmitri Mendeleev: Russian chemist who made the first periodic table, organized it by atomic mass

Henry Mosley then updated the periodic table to be organized by atomic number.

Periodic Law: when elements are arranged in order of atomic number, there is a periodic repetition of their chemical and physical properties.

Horizontal Rows=periods

Vertical Columns=groups

Elements in the s and p orbitals are called the representative elements

Metals are found on the left side of the periodic table

Non-metals are found on the right side of the periodic table

Metals have a high electrical conductivity and luster. They are ductile and malleable

Non-metals are non-lustrous and poor conductors

Metalloids show properties of both metals and non-metals and are found on the stair step.

Alkali Metals: Group 1A the most reactive elements

Alkaline Earth Metals: Group 2A

Other metals include transition metals, inner transition metals, and other metals.

The Lanthanide sequence is the top row of the inner transition metals

The Actinide sequence is the bottom row of the inner transition metals.

Halogens: Group 7A and are the most reactive non-metals

Nobel Gases: the last column of the periodic table, very unreactive because they have a full outer ring of electrons (8 valance electrons)

Effective nuclear charge (ENC): the attraction → opposite charges attract, electrons are pulled toward the positively charged nucleus

The more protons the greater the effective nuclear charge

Electron shielding: the repulsion → like charges repel

Shielding increases down a group and is constant across a period

Atomic Size:

Atomic size increases down a group and right to left across the period

As you go down a group more energy levels cause the atom to be larger

Electrons in closer energy levels cause less pull to electrons outside

Across a period no energy is added but more protons making the atom smaller

Valence Electrons:

Valence electrons increase from left to right across a period and stay the same as you go down a group

Cation: Positivly charged atom

Anion: negatively charged atom

Oxidation Number:

The oxidation number is the charge that an element has after it becomes an ion

Metals tend to lose elections to get a positive charge

Non-metals tend to gain elections to get a negative charge

Ion Size:

Same trend as atomic size except anions are always bigger than cations

This is because the anions have more electrons than the atom is made from so there will be more repulsion between them causing an increase in the radius

Ionization Energy:

the amount of energy it takes to pull an electron from the outside shell of an atom

Increases up a group

increases left to right across a period

As you go down a group the valence electrons are farther away from the nucleus and so it takes less energy to pull them away from the atom

The more electrons in the outside energy level the less eager an atom will be to lose an electron.

Electronegativity:

The electronegativity of an element is the tendency for the atom to attract an electron when combining with other elements.

The scale is based on ionization and is used to predict the type of bonds

Increases up a group and increases from left to right across a period

The exception is that noble gasses have an electronegativity of 0 since they already have a full outer shell.