The Periodic Law says: PERIODIC LAW states that when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

Trends in the periodic table: Atomic Radius Ionization Energy Electron Affinity Electronegativity Metallic character

Atomic Radius } Radius this is half the distance between the centres of two atoms of that element.

ALL Periodic Table Trends Influenced by three factors: 1. Energy Level Higher energy levels are further away from the nucleus. 2. Charge on nucleus (# protons) More charge pulls electrons in closer. (+ and – attract each other) 3. Shielding effect (blocking effect?)

#1. Periodic trends in atomic radius H Going down a group the atomic radius increases because… each atom has another energy level, so the atoms get bigger. Li Na K The number of energy levels increases as you move down a group as the number of electrons increases. Each subsequent energy level is further from the nucleus than the last. Therefore, the atomic radius increases as the group and energy levels increase. Rb

#1. Atomic Size - Period Trends Going from left to right across a period, the size gets smaller. Elements have same energy levels but, there is more nuclear charge so outermost electrons are pulled closer. WHY? - As you go across a period, electrons are added to the same energy level. At the same time, protons are being added to the nucleus. The concentration of more protons in the nucleus creates a "higher effective nuclear charge." In other words, there is a stronger force of attraction pulling the electrons closer to the nucleus resulting in a smaller atomic radius. Na Mg Al Si P S Cl Ar

Ions An ion is an atom (or group of atoms) that has a positive or negative charge due to the transfer of electron/s between atoms. Atoms are neutral because the number of protons equals electrons

Ions Metals tend to LOSE electron/s, from their outer energy level to form positively charged ion = “cation” Cations are smaller than the atom they come from because not only do they lose electrons, they lose an entire energy level.

Ions Nonmetals tend to GAIN one or more electrons and become negative ion called “anions” Anions are bigger than the atom they come from because they have the same energy level, but a greater area the nuclear charge needs to cover

Shielding The shielding effect is the decrease in attraction between an electron and the nucleus in any atom.

04/10/99 Core charge Core charge is the effective nuclear charge experienced by an outer shell electron. Can be found by subtracting the number of inner-shell electrons from the nuclear charge.

#2. Trends in Ionization Energy Ionization energy is the energy required to remove outer electron from an atom in its gaseous state The energy required to remove the first electron from the outer shell is called the first ionization energy.

Ionization Energy The second ionization energy is the energy required to remove the second electron. Always greater than first IE. The third IE is the energy required to remove a third electron. Greater than 1st or 2nd IE.

Ionization Energy - Group trends As you go down a group, the ionisation energy decreases because... The electron is further away from the attraction of the nucleus, and and thus easier to remove the outermost one. There is more shielding.

Ionization Energy - Period trends Going across a period, ionisation energy generally increases from left to right because….. the atomic radius decreases, that is, the atom is smaller. The outer electrons are closer to the nucleus and more strongly attracted to the centre. Therefore, it becomes more difficult to remove the outermost electron. Exceptions at full and 1/2 full orbitals.

#3. Periodic trends in Electronegativity Electronegativity is the tendency for an atom to attract electrons to itself when it is chemically combined with another element. They share the electron, but how equally do they share it? An element with a big electronegativity means it pulls the electron towards itself strongly!

Electronegativity Group Trend As you go down a group the electronegativity decreases because… The further down a group, the farther the electron is away from the nucleus, thus, more willing to share.

Electronegativity Period Trend As you move across a period, electronegativity generally increases from left to right because….. At the right end are the nonmetals. They want more electrons.

Electronegativity is related to ionization energy Electronegativity is related to ionization energy. Electrons with low ionization energies have low electronegativities because their nuclei do not exert a strong attractive force on electrons. Elements with high ionization energies have high electronegativities due to the strong pull exerted on electrons by the nucleus.

Periodic trends in electron affinity 04/10/99 Periodic trends in electron affinity electron affinity describes the ability of an atom to accept an electron. Electron affinity increases from left to right within a period. This is caused by the decrease in atomic radius. Electron affinity decreases from top to bottom within a group. This is caused by the increase in atomic radius. Unlike electronegativity, electron affinity is a quantitative measure that measures the energy change that occurs when an electron is added to a neutral gas atom. When measuring electron affinity, the more negative the value, the more of an affinity to electrons that atom has.

Summary of Periodic Table Trends