1. Summary of the Atom
atoms are the smallest particles that can be uniquely associated with an element
Atoms cannot break down further by chemical means.
each element has unique atoms
atoms are composed of e-, p and n
atoms are electrically neutral (# of e- = # of p)
for a single element, isotopes differ only in number of n (neutrons)
atoms have characteristic masses (atomic weights)
atoms combine with one another in definite, whole number proportions to make compounds

2. ~ 10-10 m electron nucleus Mass > 10-26 kg Mass 9 x 10-31 kg
Here we have arrived at the usual pictorial conception of an atom. It is a misleading picture, but a good aide memoir .
Size 1 angstrom unit m.
Components electrons negative charge. Very light
at centre the nucleus positive to balance the electron charge
essentially all the mass.
It’s the nucleus we want to talk about . So let’s look a little closer at it.

3. ~ 1 – 7 x m (1 – 7 fermi)
The nucleus is times smaller than the atom, and as we said contains essentially all the mass. You can now see that the usual picture of the atom is way out of scale.
A better idea of scale is given if we consider the atom to be the size of the Sydney Olympic stadium.

4. If I represented the nucleus as a small ball, and threw it into the middle of the stadium, we get a better idea of the size of the nucleus relative to the atom.

5. atoms are dominantly empty space:
The Spacious Atom
atoms are dominantly empty space:
electron orbits
If an oxygen atom had a total radius of 100 km, the nucleus would be a ~1 m diameter sphere in the middle.

6. Electrons in Orbit
In a simplistic model, electrons float around the nucleus in energy levels called shells.
electron orbits
As the number of electrons increases, they start to fill shells farther out from the nucleus.
In most cases, electrons are lost or gained only from the outermost shell.

7. Atom
Nucleus
Not a European football field, but a real Australian rules footy field
This is the Melbourne CG, and is the size of the

8. Most of the atom is…
empty space!

9. The Nuclear Model
of the atom

10. Mass of an electron is approximately 1/1840th of a proton or neutron.
Mass of a neutron is very close to the mass of a proton.
1 atomic mass unit (amu or u)=
x10-24g
1 g= x1023amu
amu is defined by assigning a mass of exactly 12 amu to an atom of C-12 isotope.

11. 1 amu (atomic mass unit) is…
1/12th of the mass of one carbon-12 atom.

12. Most of the mass of the atom is…
formed by the nucleus.

13. Subatomic Particles Particle Symbol Charge Relative Mass(unit)
Electron e
Proton p
Neutron n

14. Atomic Number, Z (nuclear charge)
is the total number of protons in the atom.
Symbol
11Na
Atomic Number
Atoms are identified by their proton numbers.

15. All atoms of an element have the same number of protons11 Na
11 protons
Sodium

16. Number of Electrons If an atom is neutral ;
The net charge on the atom is zero
Number of protons = Number of electrons
Atomic number = Number of electrons in a neutral atom

17. Ions
have a net electrical charge since the total number of electrons isn’t equal to the number of protons.
can be anions (e->p+ ;formed as a result of gaining electrons; negatively charged), cations (p+>e-;formed as a result of losing electrons; positively charged).
e- + q(charge of the ion) = proton number

18. In chemical rxns, atoms never gain or lose protons
In chemical rxns, atoms never gain or lose protons. It’s the interaction of electrons.

19. Mass Number, A (nucleon number)
Counts the number of
protons and neutrons
in an atom
A= p+ + n0
Protons and neutrons (together) are called “nucleons.”

20. 11 Atomic Symbols 23Na (A)mass number (Z)atomic number sodium-23
Show the mass number and atomic number
Give the symbol of the element
(A)mass number
23Na 11
(Z)atomic number
sodium-23

21. 12C 13C C Notation for Atoms only one isotope of carbon
all isotopes of carbon

22. Basic Definitions “atomic number” = number of protons in the nucleus;
“mass number” = sum of protons + neutrons in the nucleus
“isotopic mass” = mass of a single isotope

23. 16 31 65 8 15 30 More Atomic Symbols O P Zn 8 p+ 15 p+ 30 p+
O P Zn
8 p p+ 30 p+
8 n 16 n 35 n
8 e e e-

24. Learning check For the ion find Nuclear charge Mass number
Electron number
Neutron number

25. Learning check
Find the value of unknown quantities in the table given below.
b) Classify each particle, X, Y, and Z as Cation, Anion and Neutral atom.

26. Homework!
Prepare the flash cards having the symbol of the atom on one side and the name on the other side for the first 20 elements on Page 33 in your textbook.

27. Isotopes
Atoms with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers
Isotopes of chlorine
35Cl 37Cl
chlorine chlorine - 37

28. Isotopes of Hydrogen element
has the biggest abundance in nature.

29. Learning Check 1 An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) ) ) 65
B. Number of neutrons in the zinc atom
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) ) ) 67

30. Solution An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67

31. Learning Check 2
Write the atomic symbols for atoms with the following:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________

32. Solution B. 17p+, 20n, 17e- 37Cl 17 47 16O A. 8 p+, 8 n, 8 e- 8
C. 47p+, 60 n, 47 e- 107Ag 47

33. Learning Check 3 16 14 14 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

34. Solution 14 An atom has 14 protons and 20 neutrons.
A. It has atomic number
1) 14
B. It has a mass number of
3) 34
C. The element is
1) Si
D. Another isotope of this element would be
3) 36X 14