Periodic trends

10/23/15

Atomic mass

• Atomic Mass: the average mass of one atom of an element measured in amu

• Generally the atomic mass increases down a group and from left to right

• As the amount of protons and neutrons increase, so does the mass

Atomic radius• Atomic radius: the distance from the

center of the atom to the outer edge measured in Å

• Radius increases down the group– More energy levels causes volume to

increase• Decreases across the period – Same energy level but more protons pull

electrons closer and decrease the volume

Ionic radius

• When an atom looses an electron to become positively charged, its radius decreases– More protons than electrons so strong attraction

to the nucleus• When an atom gains an electron to become

negatively charged, its radius increases– More electrons than protons so less attraction to

the nucleus

Ionization energy

• Ionization energy: the amount of energy it takes to remove an electron measured in V

• Decreases down a group– Bigger size atom makes it

easier to remove electrons• Increases across a period– Smaller size atom makes it

harder to remove electrons

Electronegativity

• Electronegativity: within a covalent compound the pull an element has for the bonded electrons

• Generally decreases down a group – Attraction for electrons in a bond is difficult because of

larger size• Increases across period– Smaller size makes easier to attract electrons

• Noble gases don’t have electronegativity values because they don’t form compounds

Density

• Density: the mass per volume measured in g/mL

• Doesn’t have as nice of a pattern• Mostly increases down group• Varies because of differences in mass and

volume trends. D=m/V

Melting point

• Melting point: the temperature the element goes from a solid to a liquid in K

• Mostly decreases down a group• Increases across metals and decreases across

nonmetals• Many different factors affect melting point

mostly related to the attraction between particles of the substance