Learning Goal #3: Discriminate between the relative size, charge, position, and number of protons, neutrons, and electrons of different elements.

Atom: the smallest unit of matter that retains the identity of the substance

http://learn.genetics.utah.edu/content/begin/cells/scale/ The nucleus has a diameter 10,000 times smaller than the

atom. The great amount of empty space in an atom can be illustrated by the following analogy.

Imagine the nucleus to be the size of a golf ball. Then on this scale the first electron shell would be about one kilometer from the golf ball, the second shell about four kilometers, the third nine kilometers and so on. If you find that hard to visualize then try this. The period at the end of this sentence, (depending on your monitor and the font you are using), is probably about 1/2 a millimeter in diameter. If that period represents the nucleus then the electrons in the first shell would be orbiting with a diameter about 50 meters around you. in fact, the actual diameter of an atom is very small and it would require some two hundred million of them side by side to form a line a centimeter long.

Atoms are composed of 2 regions: Nucleus: the center of the atom that

contains the mass of the atom Electron cloud: region that surrounds

the nucleus that contains most of the space in the atom Nucleus

Electron

Cloud

The nucleus contains 2 of the 3 subatomic particles:

Protons: positively charged subatomic particlesNeutrons: neutrally charged subatomic particles

The 3rd subatomic particle resides outside of the nucleus in the electron cloud

Electron: the subatomic particle with a negative charge and relatively no mass

Atomic ParticlesAtomic Particles

Particle Charge

Mass #

Location symbol

Electron

-1 0 Electron cloud

e-

Proton +1 1 Nucleus p+

Neutron

0 1 Nucleus n0

Protons and neutrons are in the tiny positively charged nucleus accounting for most of the mass of the atom

The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus

In an atom: The # of protons = The # of electrons

If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral

The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

An atom with 6 protons = Carbon An atom with 8 protons = Oxygen An atom with 20 protons =

Calcium

ATOMIC STRUCTUREATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom

HeHe22

44 Atomic mass

Atomic number

Number of electrons = Number of protons

Number of neutrons = Atomic mass – Number of protons

Li has a mass number of 7 and an atomic number of 3 Protons = 3 (same as atomic #) Neutrons= 7-3 = 4 (mass # - atomic

#) Ne has a mass number of 20 and

an atomic number of 10 Protons = 10 Neutrons = 20 - 10= 10

The electrons are equal to the number of protons So e- = p = atomic #

Ex: He has a mass # of 4 and an atomic # of 2 p+ = 2 no = 2 e- = 2

Cl has a mass # of 35 and an atomic # of 17 p+ = 17, no = 18, e- = 17

K has a mass # of 39 and an atomic # of 19 P+ = 19, no = 20 e- = 19

Bohr Model of the atom:All of the protons and the neutrons

The 1st ring can hold up to 2 e-

The 2nd ring can hold up to 8 e-

The 3rd ring can hold up to 8 e-

The 4th ring and any after can hold up to 18 e-

ATOMIC STRUCTUREATOMIC STRUCTURE

Electrons are arranged in Energy Levels

or Shells around the nucleus of an atom.

• first shell a maximum of 2 electrons

• second shell a maximum of 8

electrons

• third shell a maximum of 8

electrons

Mass # = 12 atomic # = 6

p+ = 6 no = 6 e- = 6

6 p and 6 n live in the nucleus

A unit created to describe atoms because the gram and kilogram are too large to use to define an atom.

1amu = 1.66 x 10-24g .00000000000000000000000166g

Listed on the periodic table as the atomic mass.

The average mass of all of the isotopes of an atom.

Element amu

Hydrogen 1.008

Carbon 12.01

Nitrogen 14.01

Oxygen 16.00

Sodium 22.99

Aluminum 26.98

1 atom = 1 amu Example

› 1 atom of carbon = 12.001 amu of carbon› 3 atoms of carbon = 36.003 amu of carbon› 3.00 X 1020 amu =2.50 x 1019 atoms of

carbon

The unit all chemists use in describing numbers of atoms.

Defined as the number equal to the number of carbon atoms in 12.01 grams of carbon.

A sample of on element with a mass equal to that element’s average atomic mass expressed in grams contains 1 mol of atoms.

6.022 X 1023

One mole of something consists of 6.022 X 1023 units of that substance.

› One mole of eggs is 6.022 X 1023 of eggs.

Elements # of atoms

Mass of sample (g)

Aluminum 6.022 X 1023 26.98

Gold 6.022 X 1023 196.97

Iron 6.022 X 1023 55.85

Sulfur 6.022 X 1023 32.07

Boron 6.022 X 1023 10.81

Xenon 6.022 X 1023 131.3

The mass of one mole of a substance.› The sum of all the

masses of the atoms in a compound.

CH4C - 1x12.01=12.01H – 4x1.008=4.032Total = 16.04g