1. Atomic Structure

2. The Atom An atom consists of a nucleus (of protons and neutrons)
electrons in space about the nucleus.
Electron cloud
Nucleus

3. Subatomic Particles 3 quarks = 1 proton or 1 neutron He Quarks
component of protons & neutrons
6 types He
3 quarks = 1 proton or 1 neutron

4. Subatomic Particles equal in a neutral atom Atomic Number
NUCLEUS
ELECTRONS
equal in a neutral atom
PROTONS
NEUTRONS
NEGATIVE CHARGE
QUARKS
Atomic Number
equals the # of...
POSITIVE CHARGE
NEUTRAL CHARGE
Most of the atom’s mass.

5. Copper atoms on silica surface.
An _____ is the smallest particle of an element that has the chemical properties of the element.
Copper atoms on silica surface.
Distance across = 1.8 nanometer (1.8 x 10-9 m)

6. ATOM COMPOSITION The atom is mostly empty space
protons and neutrons in the nucleus.
the number of electrons is equal to the number of protons.
electrons in space around the nucleus.
extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

7. ATOMIC COMPOSITION Protons (p+) Electrons (e-) Neutrons (no)
+ electrical charge
mass = x g
relative mass = atomic mass units (amu) but we can round to 1
Electrons (e-)
negative electrical charge
relative mass = amu but we can round to 0
Neutrons (no)
no electrical charge
mass = amu but we can round to 1

8. Atomic Symbols
Show the name of the element, a hyphen, and the mass number in hyphen notation
sodium-23
Show the mass number and atomic number in nuclear symbol form
mass number
23 Na
atomic number

9. Atomic Number, Z
All atoms of the same element have the same number of protons in the nucleus, Z 13
Atomic number Al
Atom symbol
26.981
AVERAGE Atomic Mass

10. Mass Number always a whole number NOT on the Periodic Table!
mass # = protons + neutrons
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always a whole number
NOT on the Periodic Table!
it is the AVERAGE atomic mass on the table

11. Mass Number, A
C atom with 6 protons and 6 neutrons is the mass standard
= 12 atomic mass units
A boron atom can have A = 5 p n = 10 amu

12. Mass # Atomic # Isotopes Nuclear symbol: Hyphen notation: carbon-12
Atoms of the same element with different mass numbers.
Nuclear symbol:
Mass #
Atomic #
Hyphen notation: carbon-12

13. Isotopes
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14. Two isotopes of sodium.

15. Isotopes & Their Uses
Bone scans with radioactive technetium-99.

16. Isotopes?
Which of the following represent isotopes of the same element? Which element?
234 X X 235 X 238 X

17. Counting Protons, Neutrons, and Electrons
Protons: Atomic Number (from periodic table)
Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible)
Electrons:
If it’s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -)
If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

18. Learning Check – Counting
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.
12C C 14C
#p+ _______ _______ _______
#no _______ _______ _______
#e- _______ _______ _______

19. Answers
12C C 14C #p
#no #e

20. Learning Check An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) ) ) 34
B. Its mass number is
C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X

21. One Last Learning Check
Write the nuclear symbol form for the following atoms or ions:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 46 e- ___________

22. Relative Atomic Mass atomic mass unit (amu)
12C atom = × g
atomic mass unit (amu)
1 amu = 1/12 the mass of a 12C atom
1 p = amu 1 n = amu 1 e- = amu
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23. Isotopes 17 37 20 Chlorine-37 atomic #: mass #: # of protons:
# of electrons:
# of neutrons: 17 37 20

24. Average Atomic Mass Avg. Atomic Mass weighted average of all isotopes
on the Periodic Table
round to 2 decimal places
Avg.
Atomic
Mass

25. 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
16.00
amu

26. Average Atomic Mass 35.40 amu
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
35.40 amu

27. ELEMENTS THAT EXIST AS DIATOMIC MOLECULES
Remember:
BrINClHOF
These elements only exist as PAIRS. Note that when they combine to make compounds, they are no longer elements so they are no longer in pairs!