Dr Sharipah Ruzaina Syed Aris

Symbols, formula, Periodic Table, Avogadro number

Symbols: Abbreviations for the chemical elements

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

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

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)

Modern Periodic Table with group labels and chemical families identified

Note: Placement of elements 58 – 71 and 90 – 103 saves space

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

Classification as metals, nonmetals, and metalloids

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

chromium A Dictionary of Architecture and Landscape Architecture |

2000 | JAMES STEVENS CURL | © A Dictionary of Architecture and Landscape Architecture 2000, originally published by Oxford University Press 2000. (Hide copyright information) Copyright

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.

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, NA.

NA = 6.02 x 1023

a mole represents 6.02 x 1023 particles

1 mol H atoms = 6.02 x 1023 H atoms 1 mol O atoms = 6.02 x 1023 O atoms 1 mol H2 molecules = 6.02 x 1023 H2 molecules 1 mol H2O molecules = 6.02 x 1023 H2O molecules

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 1023 H atoms in 1.008 g H atomic mass H = 1.008 amu6.02 x 1023 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

Using water (molar mass 18.015) as an example: 1 mole H2O 6.022 x 1023 molecules H2O

1 mole H2O 18.015 g H2O

18.015 g H2O 6.022 x 1023 molecules H2O Within chemical compounds, moles of

atoms always combine in the same ratio as the individual atoms themselves so: 1 mole H2O 2 mole H

1 mole H2O 1 mole O

1 mol of sodium atoms contains 6.022 x 1023 atoms of sodium and has a mass of 23 g.

1 mol of oxygen molecule contains 6.022 x 1023 molecules of oxygen and has a mass of 32 g.

1 mol of carbon dioxide contains 6.022 x 1023 molecule of carbon dioxide and has a mass of 12+32 =_____ g.

1 mol of sodium chloride contains 6.022 x 1023 formula unit and has a mass of =58.5 g (_____+ ______)g.

Na+ ion = 6.022 x 1023 Cl- ion = 6.022 x 1023

1 mol of calcium chloride contains 6.022 x 1023 formula unit and has a mass of =111g (_____+ ______)g.

Calcium ion = 6.022 x 1023 2 chloride ion = 2 x 6.022 x 1023

No. of particles (atoms/molecules/ions) = n x NA

n = mass/molecular weight

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?