1. Atoms and Elements

2. Structure of an Atom Charges Location in Atom Electron – negative
Orbits
Charges
Electron – negative
Proton – positive
Neutron - neutral
Location in Atom
Electrons – in orbits
Protons & Neutrons – in nucleus
Nucleus

3. Elements Pure chemical substances made up of one type of atom
Building blocks of matter
Over 115 elements known - and more being discovered

4. Elements – Symbol / Name
Symbol: one or two letter abbreviation
Examples: Latin C Carbon Au Gold-aurum O Oxygen Lb Lead-plumbum Mg Magnesium K Potassium-kalium Br Bromine Na Sodium-natrium

5. Elements – Atomic Number
DEFINES the element
Atoms are neutral…
so have same #
electrons (-) as
protons (+)
ALL atoms of the same element have the same number of protons.
All neutral atoms have no overall (net) charge, so … have the same number of electrons as protons
BUT… they can have different numbers of neutrons These are called isotopes of carbon

6. Elements – Atomic Mass
Calculated from Mass Number
MASS NUMBER = mass of all particles in one atom (protons, neutrons and electrons)
Measured in “atomic mass units” (amu)

7. Elements – Mass Number
MASS NUMBER = mass of all particles in one atom (protons, neutrons and electrons)
Mass of 1 proton = 1 amu Mass of 1 neutron = 1 amu Mass of 1 electron = really, really tiny!
SO… mass number = # protons + # neutrons
Carbon - 12
6 protons x 1 amu/proton = 6 amu
6 neutrons x 1 amu/neutron = 6 amu
6 electrons x really tiny mass = 0 amu
TOTAL = 6 amu + 6 amu + 0 amu = 12 amu

8. Elements – Mass Number Helium - 4 Nitrogen - 14 Atomic Number =
2 (protons) 4 amu (p + n)
Atomic Number =
Mass Number =
7 (protons) 14 amu (p + n)

9. Pause for….
Practice and Review

10. Isotopes Different versions of the same element
Same number of protons and electrons
Different number of neutrons
SO…. Mass number (# protons + # neutrons) is different
Identified by writing mass number after element name ex: Carbon-12, Carbon-13

11. NOTE: Mass number is used to name isotope
Isotopes…
Explain why the atomic mass for Lithium (atomic number 3; with 3 protons) is 6.94 ! !
Lithium protons, 3 neutrons
- mass number = 6
- 7.5% of all lithium
Lithium protons, 4 neutrons
- mass number = 7
% of all lithium
NOTE: Mass number is used to name isotope

12. Isotopes and Atomic Mass
Why the atomic mass for Lithium (atomic number 3; with 3 protons) = 6.94…
Calculation: Weighted Average (info. only):
7.5 % Lithium-6 at 6 amu
92.5 % Lithium-7 at 7 amu
(0.075 x 6 amu) + (0.925 x 7 amu) = (0.45 amu) (6.48 amu) = 6.93 amu

13. Elements – Atomic Mass
The atomic mass of an element is calculated by doing a weighted average of the mass numbers of all naturally existing isotopes.
If you round the atomic mass of an element to the nearest whole number, you get the mass number of the most common isotope.
7.0

14. Elements – Symbol / Name
Same # protons, different # neutrons
Atomic Mass
“Average” for all carbon
Calculated from mass numbers of isotopes
On the periodic table
Mass Number
Calculated for each individual isotope
Used to name the isotope
Averaged together to represent all carbon
All have same # protons

15. Elements - SUMMARY

17. Structure of an Atom Outside the nucleus electron Electron nucleus
Atomic mass 0
Charge (-)
nucleus
(containing protons
and neutrons)

18. Structure of an Atom Electrons are arranged in orbits Orbit 1 holds

19. Structure of an Atom Nucleus – the center of an atom contains… Protons
Atomic mass 1
Charge (+)
Neutrons
Charge none

20. Symbols Either 1 or 2 letters symbols
First letter Capital, second lower case
Some based on Latin name
Example Latin
C Carbon Au Gold-aurum
O Oxygen Lb Lead-plumbum
Mg Magnesium K Potassium-kalium
Br Bromine Na Sodium-natrium

21. The Periodic Table
Elements are arranged by size and chemical properties.
Rows
Period
Size
Columns
Group
Properties

22. Properties Properties are related to atomics structure.
The number of electrons in the outer most orbit (valence electrons) determine how an atom will behave in chemical reactions.