1. Atomic Structure The smallest part of an element is an ATOM
All atoms consist of subatomic particles:
Protons
Neutrons
Electrons

2. Nucleus The “core” of the atom Contains 99.9% of the mass of the atom
Protons and neutrons are found in the nucleus of an atom
Mass Number = mass of the nucleus or mass of protons + neutrons

3. Protons Positively charged particles
The number of protons identifies the element
1 proton = 1 atomic mass unit (amu)
# protons = Atomic Number (whole number)

4. Neutron Neutral Particles Found in the nucleus 1 neutron = 1 amu
# neutrons = Mass number – Atomic Number

5. Electrons Negatively charged particles Found in the electron cloud
Electrons have a very small mass, so we don’t even count it!
Electrons give atoms their chemical properties
Atoms are neutral so;
# electrons = # protons

6. Mass Number mass # = protons + neutrons always a whole number
NOT on the Periodic Table!
Neutron +
Electrons
Nucleus e-
Proton e- e-
Nucleus e- e-
Carbon-12
Neutrons 6
Protons 6
Electrons 6 e-

8. Shorthand Notation
Mass number
SYMBOL OF ELEMENT
Atomic number

9. C Isotopes Mass # Atomic # 12 6
Atoms of the same element with different mass numbers.
Different number of neutrons & different mass 12 6 C
Nuclear symbol:
Mass #
Each isotope has a different number of neutrons.
Atomic #
Hyphen notation: carbon-12; carbon-13
Courtesy Christy Johannesson

10. Isotopes Neutron + Electrons Nucleus Nucleus Proton Proton Nucleus
Carbon-12
Neutrons 6
Protons 6
Electrons 6
Electrons
The chemistry of each element is determined by its number of protons and electrons.
In a neutral atom, the number of electrons equals the number of protons.
Symbols for elements are derived directly from the element’s name.
Nuclei of atoms contain neutrons as well as protons.
The number of neutrons is not fixed for most elements, unlike protons.
Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes.
Carbon-14
Neutrons 8
Protons 6
Electrons 6
Nucleus

11. 6Li 7Li 3 p+ 3 n0 3 p+ 4 n0 2e– 1e– 2e– 1e– Nucleus Neutron Proton
Electrons +
Electrons +
Nucleus
Nucleus
Lithium-6
Lithium-7
Neutrons 3
Protons 3
Electrons 3
Neutrons 4
Protons 3
Electrons 3

12. Cl Isotopes 37 17 Cl Chlorine-37 atomic #: mass #: # of protons:
# of electrons:
# of neutrons: 17 37 20 37 17 Cl
Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes.
Courtesy Christy Johannesson

13. Element symbol – Mass number
Example
Element symbol – Mass number
Magnesium Magnesium-26
Mg-24 is atomic number 12
= 12 n0 12=p =e-
Mg-26 is atomic number 12
26-12 = 14 n =p =e-

14. Atomic Mass
Any sample of an element in nature is a mixture of isotopes of that element
Atomic Mass – average mass of all the isotopes of that element as they occur in nature
Atomic Mass is not a whole number since it is an average

15. Calculate the atomic mass of Cl.
Atomic mass (chlorine) =
(0.758)(35.0 amu) + (0.242)(37.0 amu) = 35.5 amu

16. Relative Atomic Mass 12C atom = 1.992 × 10-23 g atomic mass unit (amu)
1 amu = 1/12 the mass of a 12C atom
Neutron +
1 p = amu 1 n = amu 1 e- = amu
Electrons
Atomic mass
1. The mass of any given atom is not simply the sum of the masses of its electrons, protons, and neutrons.
2. Atoms are too small to measure individually and do not have a charge.
3. The arbitrary standard that has been established for describing atomic mass is the atomic mass unit (amu), defined as one-twelfth of the mass of one atom of 12C.
4. Most elements exist as mixtures of several stable isotopes. The weighted average is of the masses of the isotopes is called the atomic mass.
5. Electrons added or removed from an atom produce a charged particle called an ion, whose charge is indicated by a superscript after the symbol for the element.
Nucleus
Proton
Nucleus
Carbon-12
Neutrons 6
Protons 6
Electrons 6

17. Average Atomic Mass Avg. (mass)(%) + (mass)(%) Atomic Mass 100
weighted average of all isotopes
on the Periodic Table
round to 2 decimal places
Avg.
Atomic
Mass
(mass)(%) + (mass)(%) =
100
Courtesy Christy Johannesson

18. Calculating Average Atomic Mass
You will be given the mass number and the Percent Abundance (how common the isotope is in nature) of the isotope
Atomic mass = (% abundance in decimal form isotope1)(mass isotope1) +
(%abundance in decimal form isotope2)(mass isotope2)

19. Cl 17
100
Mass spectrum of chlorine. Elemental chlorine (Cl2) contains
only two isotopes: amu (75.53%) and (24.47%) 90 80
Cl-35 70
AAM = (34.97 amu)(0.7553) + (36.97 amu)(0.2447) 60
AAM = ( amu) ( amu)
AAM = amu 50
Abundance 40 30
Cl-37
Mass spectrum of chlorine. Elemental chlorine (Cl2) contains
only two isotopes: amu (75.53%) and (24.47%) 20 10 34 35 36 37
Mass

20. Average Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Avg.
Atomic
Mass
(16)(99.76) + (17)(0.04) + (18)(0.20)
16.00
amu = =
100
Courtesy Christy Johannesson

21. Average Atomic Mass (35)(8) + (37)(2) 10 Avg. Atomic = = Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Avg.
Atomic
Mass
(35)(8) + (37)(2) = =
35.40 amu 10
Courtesy Christy Johannesson

22. Example
Carbon has 6 protons and 6 neutrons, what is Carbon’s mass number?
C-12
An isotope of Carbon has 6 protons and 8 neutrons, what is carbon’s mass number?
C-14
Remember the number of protons NEVER changes for an element!

23. Isotope Review Same element different number of NEUTRONS
Different Mass number
Same Atomic number, therefore the same number of protons and electrons

24. Isotope Applications
Complete the read around the room station activity

25. Atomic Structure ATOMS IONS ISOTOPES Differ by number of protons
Differ by number of electrons
ISOTOPES
Differ by number of neutrons

26. Electrons Electrons give elements their chemical properties
The arrangement of the electrons will determine how it reacts with other substances
Gain electron the atom becomes negative (anion)
Lose an electron the atom becomes positive (cation)

27. Humor Two atoms are walking down the street.
One atom says to the other, “Hey! I think I lost an electron!”
The other says, “Are you sure??”
“Yes, I’m positive!”
A neutron walks into a restaurant and orders a couple
of sodas. As she is about to leave, she asks the waiter
how much she owes. The waiter replies, “For you,
No Charge!!!”

28. Electrons are found in the electron cloud
The cloud has regions of space called energy levels
The first energy level holds 2 electrons
The second energy level holds 8 electrons.
The third energy level holds 18 electrons

30. Valence Electrons Are found furthest from the nucleus
Dictate the physical and chemical properties of an element
Use the periodic table to determine the number of valence electrons.
All atoms want 8 valence electrons

32. Lewis Dot Diagram A way to illustrate the number of valence electrons
Use one dot for each valence electron
Place the dot around each side of the symbol before pairing the electrons
The symbol represents the nucleus plus all the inner electrons for the element.

33. Examples
H O N F Ne

35. Electrons and Light Electrons are normally in the ground state
When the atom is given energy the electrons move to the excited state.
When the electrons lose this energy they fall back to the ground state and emit light.
Each element has a unique emission spectrum

38. Electromagnetic Spectrum
Electromagnetic Radiation –
A broad range of energetic emissions
made up of photons
Photons – bundles of energy
Travel like waves
Move at the speed of light = 3.0 x 108 m/s
Electromagnetic waves do not require a medium to move

40. Parts of the wave Amplitude – the height of the wave
Wavelength – the distance between the two successive waves
Frequency – the number of waves that pass a given reference point per second

41. Wavelength = lamda unit is nanometer
Frequency = nu in units of 1/s or s-1

42. What is the difference between these waves?