Atomic Structure

• Democritus (a Greek Professor)

• First suggested the existence of tiny

fundamental particles that make up matter

• Named atoms

• John Dalton (a scientist)

• Studied the ratios in which elements combine

in chemical reactions

• Based his ideas on results of his experiments

1. All elements are composed of tiny particles called atoms.

2. Atoms of the same element are identical.

3. The atoms of a given element are different from those of any

other element

4. Atoms of one element can combine with atoms of other

elements to form compounds. A given compound always has

the same relative number and type of atoms

5. Atoms are indivisible in chemical processes. A chemical

reaction simply changes the way the atoms are grouped

together

• Symbol- H

• Gas

• Symbol- He

• Gas

• Symbol- Li

• Solid- metal

• Symbol- Be

• Solid

• Symbol- B

• Solid

• Symbol- C

• Solid

• Symbol- N

• Gas

• Symbol- O

• Gas

• Symbol- F

• Gas

• Symbol- Ne

• Gas

• Symbol- Na

• Symbol from natrium, Latin word for sodium carbonate.

• Solid

• Symbol- Mg

• Solid

• Symbol- Al

• Solid

• Symbol- Si

• Solid

• Symbol- P

• Solid

• Symbol- S

• Solid

• Symbol- Cl

• Gas

• Symbol- Ar

• Gas

• Symbol- K

• Name from Kalium, Latin word for alkali

• Solid

• Symbol- Ca

• Solid

• Protons

• Positively charged

• Found in nucleus

• Neutrons

• Neutral subatomic particles

• Found in the nucleus

• Electrons

• Negatively charged

• Found outside the nucleus (shells, energy levels, electron cloud, orbitals)

• The mass of electrons is negligible

• Atomic Number

• The number of PROTONS in the nucleus of the atom

• The atomic number identifies the element

• Atoms are electrically neutral

• # of PROTONS = # of ELECTRONS

• Mass Number

• The total number of PROTONS and NEUTRONS in the

nucleus of an atom

• How many protons, neutrons and electrons are in an atom of

Be-9?

• Protons = 4 Electrons = 4 Neutrons = 5

• How many protons, neutrons and electrons are in an atom of

Ne – 20

• Protons= 10 Electrons= 10 Neutrons= 10

• valence electrons- are the electrons in the last shell or energy

level of an atom

• Can determine by looking at the periodic table

• What is the appropriate number of valence electrons for the

following elements:

• H

• P

• F

• Ar

• C

• Allows you to see how atoms of one element will react

• Represent the atoms and the electrons in their outer energy levels.

• An electric dot diagram is the symbol for the element

surrounded by as many dots as there are electrons in its outer

energy level.

• Shows how many valence electrons there are.

• The dots are written in pairs on four sides of

the element symbol.

• Start by writing one dot on the right of the

element symbol.

• The second electron also goes on the right

• Starting with the 3rd electron, work your way

around the element symbol

X

1 2

3 6

4 7

5 8

• Use electron dot diagrams to show how atoms bond with each

other.

• A chemical bond is the force that holds two atoms together.

• Atoms bond with other atoms in such a way that each atom becomes more

stable.

• The outer energy levels will resemble those of the noble gases.

• Any “free” electron will want to be paired.

• If electrons are not paired, atom is reactive.

• If outer shell is not full, an ion may form.

• Atoms want all shells to be full and will gain/lose electrons to ensure this.

• Atoms are composed of 2 regions:

• Nucleus: the center of the atom that contains the mass of the atom

• Electron cloud (energy level): region that surrounds the nucleus that

contains most of the space in the atom

• 3-D

Nucleus Electron

Cloud

• Bohr Model of the atom:

• Reviewers think this could lead to misconceptions!

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 18 e-

The 4th ring and

any after can

hold up to 32 e-

• Mass # = 12 atomic # = 6

p+ = 6 no = 6 e- = 6

6 p and 6 n live in

the nucleus

• Symbol- Cu

• Symbol - Ag

• Symbol- Au

• Symbol- Sn

• Symbol- Sr

• Symbol- Cs

• Symbol- Ba

• Symbol- Br

• Symbol- I

• Symbol- Ni

• Symbol- Hg

• Symbol- Fe

• Symbol- Pb

• Symbol- Zn

• Symbol- U

• Symbol- Co

• Symbol- Pt

• Symbol- Cr

• Symbol - Sb

• Symbol – As

• Arsenic Poisoning

• Symbol - Bi

• Symbol- Cd

• Symbol- Fr

• Symbol- Kr

• Symbol- Mn

• Symbol- Rd

• Symbol- Rn

• Symbol- Ti

• Symbol- W

• Symbol- Xe

• Atoms want to have 8 valence electrons- stable

• But not all elements have 8 valence electrons…

• Therefore some atoms become ions…

• An atom or group of atoms that have a positive or negative

charge

• An ion has either gained or lost electrons

• Cation- a positive ion has lost electron(s)

• Anion - negative ion has gained electron(s)

• In general

• metals (Mg) lose electrons ---> cations

• nonmetals (F) gain electrons ---> anions

-1 -2 -3 +1 +2

By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.

+3

• Guess the charge for the following elements:

• Mg

• K

• F

• N

Mg +2

K +1

F -1

N -3

• State the number of protons, neutrons, and electrons in each of

these ions.

•

Protons Neutrons Electrons

39

K+

19

16

O -2

8

41

Ca+2

20

Mass #

Atomic #

• Atoms of the same element that differ in the number of neutrons

in the nucleus

• Because isotopes of an element have different numbers of

neutrons, they have different mass numbers.

• To distinguish between isotopes, look at mass numbers

• Isotopes of chlorine

35

Cl 37

Cl

17 17

chlorine - 35 chlorine - 37

• Hydrogen

• 1H- Hydrogen

1

• 2H- Deuterium

1

• 3H- Tritium 1

• Carbon

• 12C

6

• 14C

6

• Two isotopes of carbon are carbon – 12 and carbon – 14.

Write the symbol for each isotope using subscripts and

superscripts. Determine the number of protons, neutrons and

electrons for each isotope

• Two isotopes of oxygen are oxygen – 16 and oxygen – 18.

Write the symbol for each isotope using subscripts and

superscripts. Determine the number of protons, neutrons and

electrons for each isotope

• A device known as a mass spectrometer can be used to

determine the relative abundance and mass of the isotopes of

elements.

• Generates a graph showing the relative amounts of each isotope found in

the examined sample.

The data can be summarized as follows: Isotope Mass` Abundance 90Zr 90.00 amu 51.5 % 91Zr 91.00 amu 11.2 % 92Zr 92.00 amu 17.1 % 94Zr 94.00 amu 17.4 % 96Zr 96.00 amu 2.80 % atomic mass of isotope 100 %

• Change each percent to a decimal by dividing by 100.

• Multiply by the mass.

• Add it all together.

• Calculate the weighted average mass of zirconium using the

data below.

•

• Isotope Mass Abundance Weighted Mass

90Zr 90.00 amu 51.5 %

91Zr 91.00 amu 11.2 %

92Zr 92.00 amu 17.1 %

94Zr 94.00 amu 17.4 %

96Zr 96.00 amu 2.80 %