1. Chemistry B11
Chapter 3
Atoms

2. Matter Pure substances Mixtures Element Compounds Homogeneous matter
Anything that occupies
space and has mass
Pure substances
Fixed composition, cannot
be more purified
Mixtures
A combination of two
or more pure substances
Physically
Separable into
Element
Cannot be
subdivided by
chemical or
physical means
Compounds
Elements united
In fixed ratios
Homogeneous
matter
Uniform
Composition
throughout
Heterogeneous
Nonuniform
composition
Combine
Chemically
To form

3. Element: Is a substance consisting of “identical” atoms.
Cannot be separated by chemical or physical methods.
Carbon, Hydrogen, Oxygen
116 elements – 88 in nature
Compound: A pure substance made up of two or more
elements in a fixed ratio by numbers.
H2O (Water): 2 Hydrogen & 1 Oxygen
CO2: 1 Carbon & 2 Oxygen
20 million compounds

4. H2O CO Compounds Formula Identifies each element Ratios H O 2 = 1 or
2 : 1 C
1 : 1
H2O CO

5. H2O CH4 Molecular models O H H C Molecular formula Structural
Ball-and-stick
model
Space-filling C H
CH4

6. Mixtures Mixture: is a combination of two or more pure substances.
Homogeneous: uniform throughout
Air, Salt in water
Heterogeneous: nonuniform
Soup, Milk, Blood

7. Law of conservation of mass:
C + O  CO
All matter is made up of very tiny, “indivisible” particles (atoms).
All atoms of a given element have the same chemical properties.
Compounds are formed by the chemical combination of two or
more different kinds of atoms.
4. A molecule is a bound combination of two or more atoms.
Dalton’s Atomic theory

8. Monatomic Ar He
Diatomic N2 O2
Polyatomic
Element: S8
Atom

9. Atom Nucleus: positive charge Atoms are neutral.
                                                                                      
Atoms are neutral.
                                                                                      
Atomic mass unit (amu) = ×10-24 g
mass of proton = 1 amu
mass of neutron = 1 amu
mass of electron = 5.48×10-4 amu

10. C Atom Mass number (A): Protons + Neutrons Atomic number (Z): Protons12 6
Mass number
Atomic number

11. Isotopes
Isotopes: atoms with the same number of protons and electrons but
different numbers of neutrons.
different mass numbers C 12 6 C 13 6 C 14 6
6 P + 6 N
6 P + 7 N
6 P + 8 N
Almost the same properties

12. Cl Cl Atomic Weight Cl Cl
Atomic weight: of an element is average of the masses (in amu)
of its isotopes found on the Earth. Cl 35 37 Cl Cl
34.97 amu
36.97 amu 17 17
(75.77/100 × amu) + (24.23/100 × amu) = amu Cl 17
35.45
Atomic number
Atomic weight

14. Main-group elements: 1A to 8A
Transition elements: 1B to 8B (3 – 12)
Inner transition elements: between B3 & B4
(58 to 71 and 90 to 103)
Column: same properties (main group)
Row or Period

15. VERY reactive, unstable, solid metal
Group 1A: Alkali metals
Li-Na-K-Rb-Cs-Fr
VERY reactive, unstable, solid metal
2Na + 2H2O
2NaOH + H2
2Na + Cl2
2NaCl
Group 2A: Alkali Earth metals
Be-Mg-Ca-Sr-Ba-Ra
reactive, solid metal

16. reactive, colored, gas, nonmetal
Group 7A: Halogens
F-Cl-Br-I-At
reactive, colored, gas, nonmetal
Group 8A: Noble gases
He-Ne-Ar-Kr-Xe-Rn
non reactive, stable, gas, nonmetal

17. Classification of the elements
metals
nonmetals
metalloids
metals: solid (except mercury), shiny, conductors of electricity, ductile, malleable
nonmetals: solid, liquid or gas, do not conduct electricity (except graphite)
metalloids: between metals and nonmetals

18. Metallic properties
More metallic
More metallic

19. Maximum number of electrons
Bohr model
n=1
n=2
n=3
n=4
n=5 E1 E2 E3 E4 E5
Principal energy levels or Shells
E1 = ground state: lowest energy level 32 4 18 3 8 2 1
Maximum number of electrons
Shell
Lower energy
Higher energy

20. Subshell: s p d f
Orbital: is a region of space and it can hold 2 electrons (max). s px py pz
magnetic field
paired spins

21. Subshell: s p d f s p d f 2
2+2+2=6
=10
=14

22. Maximum number of electrons
Shell
Orbitals
Maximum number of electrons 1 1s 2
2s, 2p
2 + 6 = 8 3
3s, 3p, 3d
= 18 4
4s, 4p, 4d, 4f
= 32 3 2 3d 3p 3s 2p 2s
Principal energy level
Orbitals
Energy 1 1s

23. Electronic configuration: description of the orbitals that its electrons occupy.
Orbital box diagrams
Electron configuration
H (1) 1s
1s1 1s
He (2)
1s2
Li (3) 1s 2s
1s2 2s1
C (6) 1s 2s
1s2 2s2 2p2
2px
2py
2pz

24. Noble gas notation 1s2 2s1 Li (3) [He] 2s1 1s2 2s2 2p5 F (9)
[He] 2s2 2p5
2px
2py
2pz
Si (14) 1s 2s 3s
2px
2py
2pz
3px
3py
3pz
1s2 2s2 2p6 3s2 3p2
[Ne] 3s2 3p2

25. Valence shell: outer shell
Valence electrons: outer-shell electrons
Cl (17)
1s2 2s2 2p6 3s2 3p5
7 valence electrons
Ar (18)
1s2 2s2 2p6 3s2 3p6
8 valence electrons
C (6)
1s2 2s2 2p2
4 valence electrons
1s2 2s2 2p6
8 valence electrons
Ne (10)
Noble gases
Filled valence shells

26. For Main-group elements:
Elements in the same column (group) have the same number of
electrons in their valance shells.
The same chemical and physical properties
And form the same number of bonds.

27. Lewis dot structure Cl H He Li C
1A A A A A A A A

28. Main groups elements
s, p
Transition elements
s, p, d
Inner transition elements
s, p, d, f

29. Atomic Size
Size of an atom: is the size of its outermost occupied orbital. d

30. Ionization Energy Li + energy → Li+ + e- ion
Ionization energy: the energy required to remove the most
loosely held electron from an atom in the gaseous state.
Ionization energy
Ionization energy