1. ATOMS & ELEMENTS

2. (Greek for indivisible)
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
He divided an element into halves until it could no longer be divided and called the units …
ATOMA
(Greek for indivisible)

3. HISTORY OF THE ATOM 1808 John Dalton ATOMS
suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them
ATOMS

4. MATTER
any physical object that has mass and takes up space
ELEMENT
all atoms are identical
ATOMS
the smallest particles that represent the properties of an element

5. HISTORY OF THE ATOM Joseph John Thompson 1898
found that atoms would eject a smaller negative particle which he called an
ELECTRON

6. HISTORY OF THE ATOM 1904 Joseph John Thompson
He described atoms as a soup of positive charges to balance the electron's charge, like plums surrounded by pudding.
PLUM PUDDING
MODEL

7. HISTORY OF THE ATOM Ernest Rutherford 1910
fired Helium nuclei at a piece of gold foil which was only a few atoms thick.
although most of helium nuclei passed through, some bounced back.
Rutherford’s new evidence allowed him to propose a more detailed model with a central positive nucleus surrounded by electrons.

8. ATOMIC STRUCTURE: Particles
By 1910, we envisioned atoms as being made up of these three subatomic particles
Sub-atomic Particle
Location
Charge
Mass
p: proton
nucleus
+ charge
1 amu
n: neutron
nucleus
No charge
1 amu
outside nucleus
- charge
.0005 amu
e-:electron

9. ATOMIC STRUCTURE: Mass
most of mass is in nucleus
protons and neutrons have the same mass (~1 amu)
electrons have such a small mass that they have only a small effect on the mass of an atom

10. ATOMIC STRUCTURE: Charge
Nucleus has a positive charge (protons + neutrons = +)
Charge of protons and electrons cancel each other out!
Atoms on the periodic table have zero charge because the #p = # e-, so the # + = # -

11. He ATOMIC STRUCTURE: AZX Notation 4 2
Atomic mass
#p + #n 2
Atomic number
# protons
# of electrons = # of protons in a NEUTRAL atom

12. HISTORY OF THE ATOM Niels Bohr 1913
Bohr refined Rutherford's idea by adding that the electrons were in orbitals or energy levels.
Each orbital was only able to contain a set number of electrons.

13. ATOMIC STRUCTURE Electrons move around the nucleus
Energy level = amount of energy used by electron to go around the nucleus (orbitals = path shape, a quantum trait)
Each energy level has set number of electrons
p orbital
s orbital
Each electron is unique for that atom- no two have the same 4 characteristic traits (study of these traits = QUANTUM PHYSICS)

14. HELIUM ATOM
electrons in orbits
nucleus

15. HELIUM ATOM ATOM
Energy Level
proton N + - + N -
electron
neutron

16. ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or shells around the nucleus of an atom.
1st energy level
2nd energy level
3rd energy level
a maximum of 2 electrons
a maximum of 8 electrons
a max of 8 (or 18) electrons

17. ELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements: 16 23 11 O Na B a) b) c) 8 11 5
2, 6
2, 8, 1
2, 3 28 35 40 Cl Si Ca d) e) f) 17 14 20
2, 8, 4
2, 8, 7
2, 8, 8, 2

18. BOHR DIAGRAMS
Bohr Diagram is a model made by Neils Bohr to show parts of atom & energy levels
Bohr diagrams aren’t accurate, but are useful in explaining atomic behavior
this is the model we will use

19. BOHR DIAGRAMS Nitrogen Write the number of p and n in the center,
Circles to show the shells.
Use a dot or “X” to show electrons, and X
Nitrogen X X X
7p 7n X 14 X 7 X

20. BOHR DIAGRAMS Cl O Draw the Bohr diagrams for the following elements;X X 35 16 Cl O a) b) 17 8 X X X X X X X X
17p 18n X X X X X X X X X
8p 8n X X X X X X X

21. ISOTOPES same # of protons, different # of NEUTRONS
different atoms of the same element have different masses
The average mass of all the isotope weights is the exact atomic mass

22. IONS same # of protons, different # of ELECTRONS
Different atoms of the same element having different CHARGES
Positive ions = cations
Negative ions = anions
Notice that the number of energy level changes!!

23. SUMMARY CHANGING PARTICLES
another
Element
Different Atomic #
Changing #p changes the atom into a different element with a new atomic number
Changing #n makes an ISOTOPE and changes the atomic mass
Changing #e- makes an ION with a new charge
Compound
or molecule
Ion
new charge
Isotope
new atomic mass

24. SUMMARY The Atomic Number of an atom = number of
protons in the nucleus; unique for each element
The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
The number of Electrons = Number of protons in neutral atom.
Electrons orbit the nucleus in energy levels.
Each energy level can only carry a set number of electrons.