Unit 4- chem review

Father of the periodic table

Dmitri Mendeleev, a Russian chemist who arranged elements by increasing atomic mass and by similar chemical properties.

How Mendeleev organized the periodic table

Mendeleev arranged elements in order of increasing atomic mass and placed elements with similar properties in the same columns (groups). He left gaps for undiscovered elements and predicted their properties.

Rows of the periodic table

Called periods; they show elements with the same number of electron shells.

Columns of the periodic table

Called groups or families; they contain elements with similar chemical and physical properties.

Family names of the periodic table

Group 1: Alkali Metals (far left); Group 2: Alkaline Earth Metals; Groups 3–12: Transition Metals (center block); Group 13: Boron Family; Group 14: Carbon Family; Group 15: Nitrogen Family (Pnictogens); Group 16: Oxygen Family (Chalcogens); Group 17: Halogens; Group 18: Noble Gases (far right).

Valence electrons

Electrons found in the outermost energy shell of an atom that determine how the element reacts chemically with others.

Why valence electrons are important

They control an element’s chemical reactivity, bonding behavior, and placement in the periodic table.

Valence electrons in Alkali Metals

1 valence electron (Group 1)

Valence electrons in Alkaline Earth Metals

2 valence electrons (Group 2)

Valence electrons in Boron Family

3 valence electrons (Group 13)

Valence electrons in Carbon Family

4 valence electrons (Group 14)

Valence electrons in Nitrogen Family

5 valence electrons (Group 15)

Valence electrons in Oxygen Family

6 valence electrons (Group 16)

Valence electrons in Halogens

7 valence electrons (Group 17)

Valence electrons in Noble Gases

8 valence electrons (Group 18, except helium which has 2)

Elements without electronegativity

Noble gases, because they have full outer electron shells and do not form bonds easily.

Example of an element without electronegativity

Neon (Ne), which has a stable, full outer shell and does not attract electrons.

Cause of atomic radius trend across a period

Atomic radius decreases from left to right across a period because the number of protons increases, pulling electrons closer to the nucleus.

What is a half life?

a half life is time it takes for half of the atom of a radioactive decay