1. General Chemistry CHEM 110 Dr. Nuha Wazzan
Chapter 2 Atoms, Molecules and Ions

2. Chapter 2 Atoms, Molecules and Ions Chang Pages 49-64 H. W. p71-73 2
Chapter 2 Atoms, Molecules and Ions Chang Pages H.W. p , 2.11, 2.12, 2.14, 2.16, 2.18, 2.26, 2.34, 2.36, 2.44, 2.46, 2.50, 2.57 (a,e,f,g,h,I,j,k,l,m), 2.58 (b,c,d,g,h,I,k), 2.59 (a,b,d,g,h,j), 2.60 (a,e,f,g,h,k),2.94

3. Chapter 2 Atoms, Molecules and Ions: Outline
Introduction
2.3 Atomic Number, Mass Number and Isotopes
2.4 The Periodic Table
2.5 Molecules and Ions
2.6 Chemical Formulas
2.7 Naming Compounds
Ionic Compounds
Molecular Compounds

4. Atoms, Molecules and Ions: Introduction
Atom: is the basic unit of an element
that can enter into chemical combination
Electron (e) (-ve charge)
Proton (p) (+ve charge)
Neutron (n) (neutral)
Subatomic Particles

5. mass p = mass n = 1840 x mass e-

6. C. neutral atoms D. different atoms
Use the following table and choose which of the species are neutral?
Atom or ion element I II
III IV V VI
Atom or ion electrons (e) 6 10 18 28 7
Atom or ion protons (p) 8 17 11 30
Atom or ion neutrons (n) 36
III and V C. II and III
IV and V D. I and VI
Use the following table and choose which of the species are negatively charged?
Atom or ion element I II
III IV V VI
Atom or ion electrons (e) 6 10 18 28 7
Atom or ion protons (p) 8 17 11 30
Atom or ion neutrons (n) 36
III and V C. II and III
IV and V D. I and VI
Atoms with the same number of electrons and number of protons are called…
Ions B. isotopes
C. neutral atoms D. different atoms

7. 2.3 Atomic number, Mass number and Isotopes
Atomic number: is the number of protons in the nucleus of each atom of an element
Atomic number (Z) = number of protons in nucleus
For a neutral atom: Number of protons = number of electrons
Mass number: is the total number of neutrons and protons present in the nucleus of an atom of an element
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Thus: the number of neutrons = A - Z

8. X H H (D) H (T) U A Z 1 2 3 235 92 238 Mass Number Element Symbol
Atomic Number H 1
H (D) 2
H (T) 3 U
235 92
238

9. Isotopes: are atoms of the same element (X) with different numbers of neutrons in their nuclei
Isotopes of Hydrogen
1 P P P
0 n n n

10. The number of electrons
Example 2.1 p50
Give the number of protons, neutrons, and electrons in each of the following species:
The Atomic number (Z)
The number of electrons
The mass number (A)
The number of neutrons 11 20
A – Z
= 20 – 11
= 9

11. Isotopes of Sodium 11 p 11 p 9 n 11 n Practice Exercise p50:
How many protons, neutrons, and electrons are in the following isotope of copper: 63Cu?
How can I get the atomic number: look at the periodic table → then find the number of p, n & e.

12. 2.4 The Periodic Table
The periodic Table: is a chart in which elements having similar chemical and physical properties are grouped together.
The elements in the modern periodic table are arranged by atomic number

13. Alkali Earth Metal
Noble Gas
Halogen
Alkali Metal
Group
Period

14. Elements are arranged by atomic number (Z)
Periods: are the horizontal rows
There are 7 Periods
Groups: are the vertical rows, elements in the same group have similar chemical and physical properties
There are 8 groups, assigned as 1A-to-8A
Also 8 groups are assigned as 1B-to-8B
Some groups are given special names:
groups 1B-to-8B are called the Transition Metals
Group 1A elements (Li, Na, K, Rb, Cs and Fr) are called Alkali Metals
Group 2A elements (Be, Mg, Ca, Sr, Ba and Ra) are called Alkaline Earth Metals
Group 7A elements (F, Cl, Br, I and At) are as Halogens
Group 8A elements (He, Ne, Ar, Kr, Xe and Rn) are called Noble Gases or Rare gasses

15. Elements in the periodic table are divided into three categories:
Metal: (in green colour, Most elements) is a good conductor of heat and electricity
Nonmetal: (in blue colour, 17 elements) is a poor conductor of heat and electricity
Metalloid: (in brown colour, 8 elements) has properties that are intermediate between those of metals and nonmetals

16. Which of these elements is most likely to be a good
conductor of electricity? 
A. N
B. S
C. He
D. Fe
Which element is the 15th element in period # 4
A. Ca
B. As
C. P
D. S

17. 2.5 Molecules and Ions
A molecule: is an aggregate of two or more atoms in a definite arrangement held together by chemical forces, a molecule may contain atoms of the same element or atoms of two or more elements. H2
H2O
NH3
CH4
2.5

18. 2.5 Molecules and Ions Molecule
Diatomic molecule: contains only two atoms
Polyatomic molecule: contains more than two atoms
O3, H2O, NH3, CH4
H2, N2, O2, Br2, HCl, CO
2.5

19. An ion: is an atom or a group of atoms
that has a net positive (+ve) or negative (-ve)
Charge.
Ion
Cation: an ion with a +ve charge (lose electron/s)
Anion: an ion with a -ve charge ( Gain electron/s)
Polyatomic anion
OH-, PO43-
Monoatomic cation
Polyatomic cation
Monoatomic anion
Cl-, Br-,S2-
Na+, K+, Mg2+
NH4+

20. Cation anion 11Na 17Cl 11 protons 11 protons 11 electrons 10 electrons

21. A magnesium ion, 12Mg2+, has 
A. 12 protons and 13 electrons.
B. 24 protons and 26 electrons.
C. 12 protons and 10 electrons.
D. 24 protons and 22 electrons.
E. 12 protons and 14 electrons.
A sulfide ion, 16S2- , has: 
A. 16 protons and 16 electrons
B. 32 protons and 16 electrons
C. 16 protons and 14 electrons
D. 16 protons and 18 electrons
E. 32 protons and 18 electrons

22. How many protons and electrons are in
13 protons, 10 (13 – 3) electrons
How many protons and electrons are in
34 protons, 36 (34 + 2) electrons

23. 2.6 Chemical Formula
1. A molecular formula: shows the exact number of atoms of each element in the smallest unit of a substance
e.g. H2O, C6H12O6

24. 2. An empirical formula: shows the simplest whole-number ratio of the atoms in a substance
The Empirical Formula may the same or different from the Molecular Formula
How can we get the Empirical Formula?
Answer: Divide all the numbers by the largest
Common devisor.
e.g. The empirical formula of H2O is H2O
e.g. the empirical formula of C6H12O6 is CH2O (divide the numbers 6, 12 and 6 by the largest common devisor 6)

25. H2O
molecular
empirical
H2O
C6H12O6
CH2O O3 O
N2H4
NH2
2.6

26. Example 2.3 p57:
Write the empirical formulas for the
following molecules:
Acetylene C2H2
Nitrous oxide N2O → N2O
Practice Exercise: C8H10N4O2
Solution:
→ CH
→ N2O
PE → C4H5N2O

27. Na+ Cl- 3. Formula of Ionic Compounds: الأيونية المركبات Cation Anion
Ionic Compounds: consist of a combination of cations and an anions.
Na Cl-
Cation
Anion

28. The ionic compound NaCl

29. The sum of the charges on the cation/s and anion/s in each formula unit must equal zero→ The formula of the ionic compound must be neutral
How to make the formula neutral?
The subscript of the cation is numerically
equal to the charge on the anion, and the
subscript on the anion is numerically equal
to the charge on the cation
قاعدة تبادل التكافؤات

30. Potassium Bromide
K Br-
قاعدة تبادل التكافؤات
KBr

31. Zinc Chloride
Zn Cl-
قاعدة تبادل التكافؤات
ZnCl2

32. Aluminium Oxide
Al O2-
قاعدة تبادل التكافؤات
Al2O3

33. Chromium Sulphate
Cr SO42-
قاعدة تبادل التكافؤات
Cr2(SO4)3

34. Mg3N2 Example 2.4 p58: Write the formula of magnesium nitride,
containing the Mg2+ and N3- ions.
Solution:
Mg N3-
Mg3N2
قاعدة تبادل التكافؤات

35. 2.7 Naming Compounds
Chemical nomenclature: is naming the chemical compounds
Compounds
Organic Compound: contain carbon in combination with elements such as hydrogen, oxygen, nitrogen and sulphur
Inorganic Compound: all other compounds
Also Inorganic compounds: CO, CO2, CS2, compounds containing CN-, CO32- & HCO3- groups

36. Metal cation + Nonmetal anion
Inorganic Compounds
Ionic Compounds
Metal cation + Nonmetal anion
Molecular Compounds
Non-metal + non-metal
Metaliod + non-metal

38. Ionic Compounds
The most reactive metals (green) and the most reactive nonmetals (blue) combine to form ionic compounds.

39. Which of these pairs of elements would be most likely to form an ionic compound? 
(a) P and Br
(b) Cu and K
(c) C and O
(d) O and Zn
(e) Al and Rb
Which of these pairs of elements would be most likely to
form a molecular compound?
Na and Br (b) C and O
Ca and O (d) Zn and O
Mg and Cl

40. Metal cation + Nonmetal anion
Inorganic Compounds
Ionic Compounds
Metal cation + Nonmetal anion
Molecular Compounds
Non-metal + non-metal
Metaliod + non-metal
Nonmetal Anion: Take the first part of the element name and add -ide
Metal Cation: takes their names from the element

41. Metals form only one type of cation:
Metal Cation: takes their names from the element
Metals form more than one type of cation (other metal cations e.g.Transition Metals)
Metals form only one type of cation:
Alkali metals
Alkali earth metals
Ag+, Al3+, Cd2+, Zn2+
Common name of metal cation: NH4+ ammonium

42. Metals form only type of cation
Metals form more than one type of cation (Transition Metals)

43. Metals form only one type of cation
Element
Name of Cation
Na Sodium
Na+ Sodium ion (or sodium cation(
K potassium
K+ potassium ion (or potassium cation)
Mg magnesium
Mg2+ magnesium ion (or magnesium cation)
Al Aluminium
Al3+ aluminium ion (or aluminium cation)

44. Metals form more than one type of cation (Transition Metals)
e.g. Iron can form two cations: Fe2+ & Fe3+
How can we name it?
Stock System: specify the charge
of the cation with Roman numerals
e.g. FeCl2 → Iron (II) chloride
FeCl3 → Iron (III) chloride
Roman numerals I
One II
two
III
Three
IIII
Four IV
Five

45. Nonmetal Anion: Take the first part of the element name and add -ide
Monoatomic anion
e.g.
Cl- Chlorine → Chloride
Br- Bromine → Bromide
O2- Oxygen → Oxide
Polyatomic anion
e.g.
OH- → Hydroxide
CN- → Cyanide
Common names for some anions:
CO32- Carbonate PO43- Phosphate SO42- Sulphate
HCO3- Bicarbonate NO3- Nitrate SO32- Sulphite

46. Monoatomic anion

48. (a) Cu(NO3)2 Example 2.5 p61: Name the following compounds:
1. Cation: Copper cation (can form two
types of cation →Stock system) →
Copper (II)
2. Anion: NO3- anion has a common name
Nitrate
Thus: the name of the compound is:
Copper (II) nitrate
قاعدة تبادل التكافؤات

49. Potasium dihydroen phosphate
(b) KH2PO4
1. Cation: K form only one type of cation
→ Potassium Note: not potassium (I)
2. Anion: H2PO4- has a common name
dihydrogen phosphate
Thus: the name of the compound is:
Potasium dihydroen phosphate

50. (c) NH4ClO3 1. Cation: NH4+ has a common name ammonium
2. Anion: ClO3- has a common name
chlorate
Thus: the name of the compound is:
Ammonium chlorate
H.W. Solve the practice exercise p62

51. (a) Mercury (I) nitrite
Example 2.6 p62:
Write chemical formulas for the following
compounds:
(a) Mercury (I) nitrite
Roman number (I) shows that mercury has
+1 charge → Hg22+
Nitrite is a common name of NO2-
Thus: the chemical formula is:
Hg2(NO2)2

52. Note:
Mercury (Hg) is the only metal has this formula when it form cation with only one positive charge :
Hg22+ NOT Hg+
The cation of two positive charges has the formula Hg2+

53. Cs2S (b) Cesium sulphide Cesium Cs is in group 1A → Cs+ Sulphide S2-
Thus: the chemical formula is:
Cs2S
قاعدة تبادل التكافؤات

54. Ca3(PO4)2 (b) Calcium phosphate Calcium Ca is in 2A Ca2+
Phosphate PO43-
Thus: the chemical formula is:
Ca3(PO4)2
قاعدة تبادل التكافؤات
H.W. Solve the practice exercise p62

55. Metal cation + Nonmetal anion
Inorganic Compounds
Ionic Compounds:
Metal cation + Nonmetal anion
Molecular Compounds
Non-metal + non-metal
Metaliod + non-metal

56. Molecular Compounds common names H2O, NH3, CH4
element further left in periodic table is 1st
element closest to bottom of group is 1st

57. Molecular Compounds How can we name it?
Place the name of the first element in the formula first, and the second element is named by adding –ide at the last of the name.
e.g.
HCl
Hydrogen chloride
HBr
Hydrogen bromide
SiC
Silicone carbide

58. In the following cases: (one pair of elements form several different compounds)
CO CO2
SO SO3
NO N2O4
How can we name these compounds?

59. How can we name these compounds?
Also by placing the name of the first element in the formula first, and the second element is named by adding
–ide at the last of the name.
+ By using of Greek prefixes to denote the number of atoms of each element present.
Thus:

60. CO Monocarbon monooxide → Carbon monoxide CO2 Carbon dioxide SO2
Note: Omitted if its in the first element CO
Monocarbon monooxide
→ Carbon monoxide
CO2
Carbon dioxide
SO2
Sulphur dioxide
SO3
Sulphur trioxide
NO2
Nitrogen dioxide
N2O4
Dinitrogen tetroxide
Note: momooxide the o is omitted
Note: tetraoxide →tetroxide the a is omitted

61. Example 2.7 p63:
Name the following molecular compounds:
(a) SiCl4
One silicon atom & four chlorine atoms
Thus: Monosilicon tetrachloride (or omit
the mono)
Thus: Silicon tetrachloride

62. Four phosphourus atoms & ten oxygen atoms
(b) P4O10
Four phosphourus atoms & ten oxygen
atoms
Thus: Tetraphosphourus decoxide
Note: decaoxide the a is omitted

63. (b) Disilicon hexabromide
Example 2.8 p64:
Write chemical formulas for the following
molecular compounds:
(a) carbon disulphide
There is one carbon atom & two sulphur
Atoms, Thus: CS2
(b) Disilicon hexabromide
There is two silicon atoms & six bromine
Atoms, Thus: S2Br6
H.W. Solve the practice exercise p64

64. Naming Compounds: Summary
1. Ionic Molecular
1. Metal Cation Non-metal Anion
Take the name of the element
Common metal NH4+
Metal form one type of cation (1A, 2A, Ag+, Cd2+, Al3+ , Zn2+)
Metal form more than one type of cation (e.g.. Cr2+ & Cr3+)
→ Stock System → Roman numerals (1 = I, 2 = II, 3 = III, 4 = IV, 5 = V)

65. Compound
1. Ionic Molecular
2. Non-metal Anion Metal Cation
Take the name of the element but change the last of the name to -ide
1. Common names, ClO4- → chlorate
2. monoatomic non-metals, e.g. chlorine → chloride
3. Polyatoic non-metals, OH- → hydroxide

66. Compound 2. Molecular 1. Ionic
Pairs form one type of compound: Pairs form several type of compounds:
Put the name of the first element
first and change the name of the
second element but change the last
of the name to -ide
e.g. HCl Hydrogen chloride
Put the name of the first element
first and change the name of the
second element but change the last
of the name to –ide, & use the Greek prefixes (mono- = 1, di- = 2 ……..)
e.g. CO carbon monoxide
CO2 carbon dioxide

67. The correct name for NH4NO3 is 
(a) ammonium nitrate.
(b) ammonium nitrogen trioxide.
(c) ammonia nitrogen oxide.
(d) hydrogen nitrogen oxide.
(e) hydrogen nitrate.
The correct name for PCl5 is 
(a) monophosphate pentachloride
(b) phosphorus chloride
(c) chlorophosphate
(d) monophosphate tetrachloride
(e) phosphorus pentachloride

68. التكافؤ او عدد الاكسده للعناصر الشهيره
Group 1A (alkaline Metals): +1
Group 2A (alkaline Earth Metals): +2
Group 3A: +3
Group 5A: -3 (= 5-8)
Group 6A: -2 (= 6-8)
Group 7A (halogens): -1 (= 7-8)

70. Problems: 2.57 & 2.58 p73:
Name these compounds:
Na2CrO4
K2HPO4
HBr
Li2CO3
K2Cr2O7
NH4NO2
PF3
PF5
P4O6
→ ionic → sodium chromate
→ ionic → potassium hydrogen phosphate
→ molecular → hydrogen bromide
→ ionic → lithium carbonate
→ ionic → potassium dichromate
→ ionic → ammonium nitrite
→ molecular → phosphorus triflouride
→ molecular → phosphorus pentaflouride
→ molecular → tetraphosphourus hexoxide

71. CdI2
SrSO4
Al(OH)3
Na2CO3
FeCl2
FeO
Fe2O3
→ ionic → cadmium iodide
→ ionic → strontium sulphate
→ ionic → aluminium hydroxide
→ ionic → sodium carbonate
→ ionic → iron (II) chloride
→ ionic → iron (II) oxide
→ ionic → iron (III) oxide

72. Problem 2.59 & 2.30 p73:
Write the formulas for the following
compounds:
Rubidium nitrite
potassium sulphide
magnesium phosphate
calcium hydrogen phosphate
potassium dihydrogen phosphate
iodine heptaflouride
→ RbNO2
→ K2S
→ Mg3(PO4)2
→ CaHPO4
→ KH2PO4
→ IF7

73. ammonium sulphate
silver perchlorate
boron trichloride
copper (I) cyanide
copper (II) cyanide
lead (II) carbonate
lead (IV) carbonate
→ (NH4)2SO4
→ AgClO4
→ BCl3
→ CuCN
→ Cu(CN)2
→ PbCO3
→ Pb(CO3)2

74. End of Chapter 2