Atomic Structure

ELEMENTS

115+ known elements90 naturally occurring elements

14 most common elements: hydrogen (H) carbon (C) nitrogen (N) oxygen (O) sodium (Na) magnesium (Mg) aluminum (Al) silicon (Si) phosphorous (P) sulfur (S) chlorine (Cl) potassium (K) calcium (Ca) iron (Fe)

CHONPS = elements important for life

ELEMENTS

all atoms of a specific element have the same number of protons

atoms of different elements have a different number of protons

arranged on Periodic Table to show trends

PERIODIC TABLE

ATOMIC SIZE

SIZE1 mL H2O =

100,000,000,000,000,000,000,000 atoms

1023 atoms …this is more than the number of

drops of water in all lakes, rivers, and streams on Earth

Special microscopes for studying atoms: transmission electron microscope scanning tunneling microscope

INSIDE AN ATOM

NUCLEUS

1 millionth of the volume of atom

99.9% of the mass of an atom

very, very dense

contains: protons

neutrons

PROTON p+

positive (+1) charge

mass = 1.673 x 10-24 g = 1 amu amu = atomic mass unit

all identical

strong nuclear force holds them together

NEUTRON n0

NO charge

mass = 1 amu

all identical

the number of neutrons can vary for a specific element

ELECTRON e-

negative (-1) charge

mass = 1/1836 of proton ≈ 0 amuelectron clouds:

space in which e- are likely to be found e- whirl around nucleus billions of times per

second impossible to find the exact position of an

electron more energy means a larger electron cloud

ATOM vs. ION

ATOM: # of protons = # of electrons NO CHARGE

ION: A charged atom e- < p+ indicates a POSITIVE ION

“CATION” e- > p+ indicates a NEGATIVE ION

“ANION”

SUBATOMIC PARTICLES

Abbreviation Charge LocationMass

(AMU)

Who?

When?

proton p+ +1 nucleus 1

neutron no 0 nucleus 1

electron e- -1 electron clouds 0

Rutherford

1919

Chadwick

1932

Thomson

1897

PERIODIC TABLE SYMBOL

Element Name

Atomic Number# of protons

Element Symbol

Atomic Mass (amu)

ATOM SYMBOL (chromium-52)

Mass Number# protons + # neutrons

Atomic Number# of protons

5224Cr

Element Symbol

ATOMIC NUMBER

“Z”

number of PROTONS

identifies the element

never, EVER changes for a given element

MASS NUMBER

“A”

number of PROTONS + NEUTRONS

mass of atom in amu (almost all mass is in the nucleus)

neutrons = mass number –atomic number

ISOTOPE

atoms of the same element that have different numbers of neutrons (different mass numbers)

similar chemical properties, but different mass

isotopes are named for their mass number, for example:

chlorine-35 35Clchlorine-37 37Cl

ISOTOPE EXAMPLE

carbon-12: 6 protons 6 neutrons

carbon-14:6 protons8 neutrons

126 C

146 C

ISOTOPE EXAMPLE

ION SYMBOL

Mass Number# protons + # neutrons

Atomic Number# of protons

5224Cr

Ion Charge

+2

this atom must have LOST 2 ELECTRONS to become a

+2 ION

POSITIVE ION CATION

atom that has lost electrons

Protons?

13Neutrons?

14Electrons?

10

2713Al +3

NEGATIVE ION ANION

atom that has gained extra electrons

Protons?

34Neutrons?

45Electrons?

36

7934Se -2