1. Chemical Foundations: Elements, Atoms, and Ions
Chemistry 101
Chapter 4
Chemical Foundations: Elements, Atoms, and Ions

2. Element: is a substance consists of identical atoms.
Cannot be divided by chemical & physical methods.
Carbon, Hydrogen, Oxygen
116 elements – 88 in nature
Millions of compound are composed of these 116 elements.

3. Element abundance on earth
Ti: 0.6%
Others: 0.9%
O - O O2
Almost half of the mass is oxygen.
20% of atmosphere.

4. Element Symbols The first letter or two first letters of element name:
Oxygen O Silicon Si
Carbon C Argon Ar
Sometimes, two letters are not the first letters:
Chlorine Cl Zinc Zn
Sometimes, old names are used (Latin or Greek):
Iron (Ferrum) Fe Lead (Plumbum) Pb

5. Dalton’s Atomic theory
All matter is made up of very tiny, indivisible particles (atoms).
All atoms of a given element have the same chemical properties.
Compounds are made up of two or more different kinds of atoms.
A compound has the same relative numbers and types of atoms.
Dalton’s Atomic theory
Law of constant composition: Compound always has the same composition.
Compound always has the same properties. H O 2 = 1 or
2 : 1 C
1 : 1
H2O CO

6. Dalton’s Atomic theory
4. Atoms are not created or destroyed in chemical reactions.
A chemical reaction changes the way the atoms are grouped together.
Law of conservation of mass:
C + O  CO

7. H2O Chemical Formula Compound Formula Identifies each element Ratios
Subscript (number of each atom)
Subscript 1 is not written.

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

9. Atom + -
(Source of  particles)

10. 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

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

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

13. 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

15. 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: the same properties (main group)
Row or Period (7 rows)

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

17. 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

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

19. They occur in compounds.
Most elements are reactive and they cannot be found in nature in free form.
They occur in compounds.
Noble metals: unrecative metals
Ag, Au, Pt
Monatomic Ar He
Diatomic N2 O2
Polyatomic S8
Noble gases

20. Buckminsterfullerene
Allotropes
Different forms of an element
Carbon:
Buckminsterfullerene
& Nanotube
Diamond
Graphite

21. Metallic properties
More metallic
More metallic

22. Ions Total number of protons = Total number of electrons
Atom is neutral (zero net charge).
Ion: atom with any charges (positive or negative).
Na → Na+ + e-
Cation
Cl + e- → Cl-
Anion
Number of protons and neutrons in the nucleus remains unchanged.

23. Na+ Na Ions & Ionization + e- Na + energy → Na+ + e- ion
11+
11-
10-
The size of the cation is smaller than the neutral atom.

24. Ions & Ionization
Cl + e- → Cl-
ion
Cl-
+ e- Cl
17-
18-
17+

25. Ionization Energy
Ionization energy: the energy required to remove the most
loosely held electron from an atom in the gaseous state.
Ionization energy
Ionization energy

26. Metals: lose 1, 2 or 3 e- Cation (Y+) Ions
Nonmetals: gain 1, 2 or 3 e-
Anion (X-)
Transition elements 1A 2A 3A 4A 5A 6A 7A 8A

27. Ionic Compounds
Ionic compounds are salts containing cations and anions.
The positive charge of the cation(s) must balance the negative charge of the anion(s) to form a neutral compound.

28. Ionic Compounds
Sometimes several cations balance one anion. Sometimes one cation needs several anions.

29. Ionic Compounds Mg → Mg2+ + 2e- Cation Cl + e- → Cl- Anion Mg2+ 2Cl-

30. Ionic Compounds Li → Li+ + e- Cation S + 2e- → S2- Anion 2Li+ S2- Li2S
Al → Al3+ + 3e-
Cation
O + 2e- → O2-
Anion
2Al3+
3O2-
Al2O3

31. MEMORIZE