Trends of the Periodic Table

Atomic radius - one half the distance between the nuclei of identical

atoms that are bonded together

Atomic Radius Trend:

1. Down a group – atomic radii increasesThis happens because of the increased number

of energy levelsThe energy levels shield the electrons from the

attraction of protons in the nucleus 2. Across a period – atomic radii decreases

This happens because as more electrons are added to the same energy level

Those electrons are pulled closer due to the increased number of protons in the nucleus

Largest atomic radii – 87 franciumSmallest atomic radii – 9 fluorine

Valence electrons - the electrons found in the outermost energy level

• These are the electrons available to be gained, lost, or shared

• All atoms want 8 valence electrons or a full outer energy level

• Valence electrons determine the chemical properties of the atom

• The group number is the number of valence electrons

Atoms are neutral because there are equal numbers of both protons and electrons

• Sometimes atoms can gain or lose electrons to form ions • An ion is an atom or group of atoms that has a positive

or negative charge

• Losing electrons results in a positive ion called a cation

• Gaining electrons results in a negative ion called an anion

Cations• Metals (left side of the table) form cations

• Cations are smaller than their atom counterparts because they are losing an electron (and sometimes an energy level)

• More positive charges have a greater pull on less negative charges

Cation formation

Anions• Nonmetals (right side of the table) form

anions • Anions are larger than their atom counterparts

because they are gaining an electron • Less positive charges cannot pull in the greater

number of negative charges

Anion formation

Ionization Energy• Ionization energy is the energy required to

remove an electron from an atom • a low IE means it is easier to remove the electron • Atoms can lose an electron, to form an ion • They do this to achieve noble gas electron

configuration (or 8 valence electrons) • When an atom easily loses electrons, it is said to

be active • Metals tend to lose electrons

Ionization Energy Trend:

1. Down a group – ionization energy decreases • As the valence electrons are farther from the

nucleus, the atom gives them up with less energy 2. Across a period – ionization energy increase • As the number of valence electrons increases in

the same energy level, the atom is more resistant to giving up an electron (more energy)

Greatest IE – fluorine Least IE - francium

Electron affinity

• Electron affinity is the energy change required to gain an electron

(released energy is a negative value) • When an atom releases a lot of energy

it is said to be active • Nonmetals tend to gain electrons

(large energy change)

Electron Affinity Trend

1. Down a group – electron affinity decreases (slightly) • Distance from the positive nucleus decreases the pull

on the electrons 2. Across a period – electron affinity increases • As the number of valence electrons added to the

same energy level increases, the atom easily accepts another electron (to reach 8)

Greatest EA – fluorine Least EA – francium

Electronegativity

Electronegativity is the measure of the ability of an atom in a chemical compound to attract electrons • All values are based on fluorine • Fluorine is most electronegative atom - 4.0 • The trend decreases in either direction from

fluorine