Atoms, Elements,and the Periodic Table

Atoms

Atoms are the building blocks of matter The modern atomic model describes an

atom as consisting of: Nucleus that contains: Protons, neutrons, and electrons

outside of the nucleus

Sub atomic Particles

Protons Found in the nucleus Have a positive charge (+) Each element in the periodic table

has its own specific number of protons

Subatomic Particles (cont.)

Neutrons Found in the nucleus Have no charge (neutral)

Subatomic Particles (cont.)

Electrons Found orbiting around the nucleus in

electron clouds The exact location of electrons

cannot be determined Electrons have a negative charge (-) In a neutral atom, the number of

electrons= the number of protons

Atomic Number Atomic number is:

The number of protons in an element

Every atom of a specific element has the same number of protons

Example: Hydrogen has 1 proton Carbon has 6 protons

Isotopes Isotopes of an element are: Elements having the same number of

protons, but different numbers neutrons

Examples: Carbon 12, 6 protons+ 6 neutrons

Carbon 13, 6 protons+7 neutrons Carbon 14, 6 protons + 8

neutrons

Mass Number Mass number is: The number of protons + neutrons

in the nucleus of an atom

The Periodic Table In 1869, Dmitri Mendeleev developed the

first periodic table based on atomic mass: (atomic mass= #protons+#neutrons in

the nucleus of the atom) In 1913, Thomas Moseley developed the

modern periodic table based on atomic number

(atomic number=#protons in the nucleus of the atom)

The Periodic Table (cont.)

Periodic means: Repeating according to a pattern The modern periodic table is arranged

in columns and rows Columns go up and down (think of

columns on a building) Rows go from left to right

The Periodic Table (cont.) Groups or Families Columns are called: Groups or Families There are 18 groups or families in the

periodic table Elements in the same group or family have

the same number of valence electrons Valence electrons are the number of

electrons in the outer most energy level Group 1 has 1 valence electron

The Periodic Table (cont.) Groups or Families Group 1 has 1 valence electron 2 2 13 3 14 4 15 5 16 6 17 7 18 8 *Groups 3-12 do not follow this pattern

The Periodic Table (cont.) Periods Periods are the portion of the periodic

table that go from left to right (think of when you write a sentence, you put a period at the end of the sentence.

There are 7 periods in the periodic table. All elements in the same period, have

the same number of energy levels. Energy levels are where the electrons

are located

The Periodic Table (cont.)