Symbols and formulas

1. Dr Sharipah Ruzaina Syed Aris
Symbols, formula, Periodic Table,
Avogadro number

2. Symbols: Abbreviations for
the chemical elements

3. Atomic Symbols, Isotopes, Numbers
X = Atomic symbol of the element
A = mass number; A = Z + N
Isotope = atoms of an element with the same
number of protons, but a different number
of neutrons
A
Z
Z = atomic number
(the number of protons in the nucleus)
N = number of neutrons in the nucleus
X
The Symbol of the Atom or Isotope

5. Chemical formulas are collections of
chemical symbols that are used to describe
elements and compounds
◦Free elements are not combined with other
elements in a compound
Examples: Fe (iron), Na (sodium), and K (potassium)
◦Many nonmetals occur as diatomic molecules

6. The Periodic Table summarizes chemical
and physical properties of the elements
The first Periodic Tables were arrange by
increasing atomic mass
The Modern Periodic table is arranged by
increasing atomic number:
Elements are arranged in numbered rows called
periods
The vertical columns are called groups or families
(group labels vary)

7. Modern Periodic Table with group labels and
chemical families identified
Note: Placement of elements 58 – 71 and 90 – 103 saves space

8. Some important classifications:
◦A groups = representative elements or main
group elements
I A = alkali metals
II A = alkaline earth metals
VII A = halogens
VIII = noble gases
◦B groups = transition elements
◦Inner transition elements = elements 58 – 71
and 90 – 103
58 – 71 = lanthanide elements
90 – 103 = actinide elements

9. Classification as metals, nonmetals, and
metalloids

10. Metals
Tend to shine (have metallic luster)
Can be hammered or rolled into thin sheets
(malleable) and can be drawn into wire (ductile)
Are solids at room temperature and conduct
electricity
Nonmetals
Lack the properties of metals
React with metals to form (ionic) compounds
Metalloids
Have properties between metals and nonmetals

11. chromium
A Dictionary of Architecture and Landscape Architecture |
2000 | JAMES STEVENS CURL | © A Dictionary of Architecture and
Landscape Architecture 2000, originally published by Oxford
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chromium. Metallic element discovered independently by Louis-
Nicolas Vauquelin (1763–1829) and Martin Heinrich Klaproth (1743–
1817) in 1798, but not isolated until 1859 by Friedrich Wöhler
(1800–82). Despite its attractive, bright, shiny, silvery appearance,
and its reluctance to corrode, it was not much used until it was
employed in the armaments industry during the 1914–18 war. From
the 1920s it was produced commercially, and was used for plating
on steel or copper (notably for the automobile industry), and was
favoured by several Modernist architects for both buildings (e.g.
Mies van der Rohe for the casings of columns in both the Barcelona
Pavilion and the Tugendhat House) and furniture (e.g. the tubular
steel frames of chairs of the period). It was widely used for
Art-Deco work.

13. Mole is defined as the amount of a
substance that contains the same number
or particles (atoms, molecules, or ions)
that exists in exactly 12.00 g of
carbon-12. Known as Avogadro constant,
N
A.
N
A =
6.02 x 10
23
 a mole represents 6.02 x 10
23
particles
1 mol H atoms = 6.02 x 10
23
H atoms
1 mol O atoms = 6.02 x 10
23
O atoms
1 mol H
2 molecules = 6.02 x 10
23
H
2 molecules
1 mol H
2
O molecules = 6.02 x 10
23
H
2
O molecules

14. Avogadro constant represents the number of
atoms of an element in a sample whose mass
in grams is numerically equal to the atomic
mass of the element. Thus these are:
6.02 x 10
23
H atoms in 1.008 g H atomic mass H = 1.008 amu
6.02 x 10
23
S atoms in 32.07 g S atomic mass S = 32.07 amu
Knowing Avogadro constant and the atomic mass of an
element, it is possible to calculate the mass of an individual
atom. You can also determine the number of atoms in a
weighed sample of any element.
Avogadro’s number links moles and atoms, or moles and
molecules and provides an easy way to link mass and atoms
or molecules

15. Using water (molar mass 18.015) as an
example:
1 mole H
2O  6.022 x 10
23
molecules H
2O
1 mole H
2O  18.015 g H
2O
18.015 g H
2O  6.022 x 10
23
molecules H
2O
Within chemical compounds, moles of
atoms always combine in the same ratio as
the individual atoms themselves so:
1 mole H
2O  2 mole H
1 mole H
2O  1 mole O

16. 1 mol of sodium atoms contains 6.022
x 10
23
atoms of sodium and has a
mass of 23 g.
1 mol of oxygen molecule contains
6.022 x 10
23
molecules of oxygen and
has a mass of 32 g.
1 mol of carbon dioxide contains
6.022 x 10
23
molecule of carbon
dioxide and has a mass of 12+32
=_____ g.

17. 1 mol of sodium chloride contains 6.022 x
10
23
formula unit and has a mass of =58.5 g
(_____+ ______)g.
Na+ ion = 6.022 x 10
23

Cl- ion = 6.022 x 10
23

1 mol of calcium chloride contains 6.022 x
10
23
formula unit and has a mass of =111g
(_____+ ______)g.
Calcium ion = 6.022 x 10
23

2 chloride ion = 2 x 6.022 x 10
23

18. No. of particles (atoms/molecules/ions)
= n x NA
n = mass/molecular weight

19. 1. Calculate :
 a) the mass of a titanium atom
 b) no. of atoms in a ten-gram sample of
the metal.
2. How many moles of nickel atom are there
in 80 nickel atoms?