C1 : 1.2-RELATIVE MOLECULAR MASS(R.M.M),Mr

RELATIVE MOLECULAR MASS(R.M.M),Mr

A mass of one molecule of a compound compared to 1/12 

mass of one atom of 12C with the mass 12.000

The relative molecular mass of a compound is the summation

of the relative atomic masses of all  atoms in  a molecular

formula.

 

Further example :

C1.2-E6 : RELATIVE ATOMIC MASS (R.A.M)

C1 : 1.2-RELATIVE ATOMIC MASS (R.A.M)

RELATIVE ATOMIC MASS (R.A.M) 

A mass of one atom of an element compared to 1/12 mass of one atom of 12C with the mass 12.000

Example : Ar H = 1, Ar O = 16, Ar Na = 23, Ar F = 19, Ar Mg = 24, Ar Br =80

EXAMPLE 1:

Average atomic mass 16O is 15.995 amu. Calculate RELATIVE ATOMIC MASS 16O .?

RELATIVE ATOMIC MASS (RAM) 16O;

EXAMPLE 2:

Ans:

Relative Atomic Mass, Ar Ag 

= [(51.84% X 106.91) + (48.16% X 108.90)] / 100 

= 107.87

EXAMPLE 3:

What is the relative atomic mass of Boron if it exists as 19.90% ¹⁰B (10.013 amu) and 80.10%¹¹B (11.009 amu)?

Ans:

1st step : Calculate average atomic mass Boron

Average Atomic Mass Boron

= [(19.90% X 10.013amu) + (80.10% X 11.009amu)] / 100 

= 10.811 amu

2nd step : Calculate relative atomic mass, Ar Boron

Relative Atomic Mass, Ar Boron

=     10.811 amu  

      1/12 x 12 amu

= 10.811

EXAMPLE 4:

Determine the relative atomic mass, A_r  of an element Z if the atomic mass ratio of Z to carbon-12 is 1.17

Ans:

EXAMPLE 5:

Copper consists of two isotopes, copper-63 and copper-65. 

Its relative atomic mass is 63.62.

Calculate the % abundance of each isotope.

Ans:

% copper-63 + % copper-65 = 100%
assume the abundance of copper-63= y% 

thus, the abundance of copper-65 = (100 - y) 

63.62 = (y/100 x 63) + [(100 - y)/100 x 65]
63.62 = 63y/100 + 6500/100 - 65y/100
6362 = 63y + 6500 - 65y
-135 = -2y
y = 69

Abundance of copper-63 = 69/100 = 69%

Abundance of copper-65 = 100 - 69 = 31%

EXAMPLE 6:
An atom of element X is 19.6 times heavier than one carbon-12 atom.  What  is the relative atomic mass of X?

Ans:
Relative atomic mass of X 
= 19.6 x mass C-12 
    1/12 x mass C-12
= 235.2

EXAMPLE 7:

Given that the percentage abundance of is 75% and that of  is 25%, calculate the Ar of chlorine.

Solution:

EXAMPLE 8:

Bromine has two isotopes, Br-79 and Br-81. Both exist in equal amounts. Calculate the relative atomic mass of bromine.

Solution:

EXAMPLE 9:

The neon element has three isotopes. They are 90.92% of , 0.26% of  and 8.82% of 

Solution:

EXAMPLE 10:

Ans:
1st step : Calculate average atomic mass Iron

2nd step : Calculate relative atomic mass, Ar Iron

Relative Atomic Mass, Ar Boron

=     55.85 amu  

      1/12 x 12 amu

= 55.85

EXAMPLE 11:

Ans:

C1 : 1.2-AVERAGE ATOMIC MASS

Most elements occur in nature as mixtures of isotopes. The average atomic mass, also called atomic mass, of an element is determined by using the masses of its various isotopes and their relative abundances.

ATOMIC MASS @ ATOMIC WEIGHT

- the mass of an atom is expressed in atomic mass units (amu or u)

- modern atomic mass standard, defined by the mass of one atom of carbon-12

- one atom of carbon-12 is assigned the mass of 12 u

- thus 1 u = 1/12 the mass of a C-12 atom

- all other atoms have a mass which is relative to this

  

ISOTOPIC ABUNDANCE

- the relative amount in which each isotope is present in an element

- expressed as a percent or as a decimal fraction

 -e.g magnesium is 79% Mg-24, 10% Mg-25 and 11% Mg-26

MASS SPECTROMETRY

- Technique used to determined relative atomic mass and the relative abundance of isotopes.

- Different atoms / isotopes / molecules can be identified by their characteristic pattern 

of lines (peak)

AVERAGE ATOMIC MASS                      

- it is a weighted average of the atomic masses of all of the naturally occurring isotopes of

an element according to their abundance. 

- this is the mass shown for an element on the periodic table

- a mass spectrometer is the instrument used to determine mass and abundance of the   

isotopes.

Example 1:

Example 2 :

C1 : 1.2-PROTON NUMBER, MASS NUMBER, IONS & ISOTOPES

What makes an atom of one element different from an atom of another element? 

Atoms of different elements contain different numbers of protons. 

For example, oxygen atom contain 8 protons; nitrogen atom contain 7 protons. 

Different elements have different atomic numbers. 

ATOMIC NUMBER (Z)

Also known as proton number

Number of protons in the nucleus of each atom of an element.

In neutral atom, number of protons  =  number of electrons

In ions, number of electrons = number of protons - (Charge)

MASS NUMBER (A)

Also known as nucleon number 

The total number of protons and neutrons present in the nucleus of an atom of an element.

Number of Neutrons   =   Mass Number (A)  –   Atomic Number (Z)

ISOTOPES NOTATION 

Most elements occur in nature as mixtures of isotopes.

Atoms with identical atomic numbers but different mass numbers are called isotopes. 

"Isotopes are  atoms of the same element, having the same number of protons in their nucleus but different number of neutrons"

Isotopes are represented by symbols such as this: . The symbol represents "carbon twelve", carbon-12. 

The atomic number is shown by the subscript and the mass number is shown by the superscript.

ATOMS 
– Differ by number of protons

IONS 
– Differ by number of electrons

ISOTOPES 
– Differ by number of neutrons

Example 1: What is the isotopic notation for the isotope carbon-14?

From the periodic table, we see that the atomic number (number of protons) for the element carbon is 6. The name carbon-14 tells us that this isotope's mass number is 14. 
Answers:
The chemical symbol for carbon is C. Now write the isotopic notation for carbon-14.

146C

We can determine the number of neutrons as 14−6=8 neutrons.

Example 2. Given the isotopic notation 4822Ti, identify the following:

a) Name of the isotope
b) Mass number
c) Atomic number
d) Number of protons
e) Number of neutrons.

Answers:

a) titanium-48
b) 48
c) 22
d) 22
e) 48−22=26

Example 3. How many protons, neutrons, and electrons are in an atom of ¹⁹⁷Au?
Answers:
The superscript 197 is the mass number, the sum of the numbers of protons and neutrons. According to the list of elements given on the front inside cover of this text, gold has an atomic number of 79. Consequently, an atom of ¹⁹⁷Au has 79 protons, 79 electrons, and 197 - 79 = 118 neutrons.

Example 4. How many protons, neutrons, and electrons are in a Si-28, Br-79, P-32 and I-125 ?
Answers:



Example 5. How many protons, neutrons, and electrons are in a ¹³⁸Ba atom?
Answers:
56 protons, 56 electrons, and 82 neutrons

Example 6. 

Determine the numbers of protons, neutrons, and electrons in each silicone isotope. ²⁸Si, ²⁹Si, and ³⁰Si.

(Refer to the periodic table for the atomic number)
Answers:

Example 7. 

Give the number of protons and electrons in each of the following common ions: 

K+, Mg2+, Fe3+, Br–, Mn2+, C4–, Cu2+.

Answers:

Numerical list of Atomic Numbers of Elements

Name of Element	Symbol of Element	Number of Protons / Electrons	Mass Number	Atomic Number	Number of Neutrons
Hydrogen  Helium  Lithium Beryllium  Boron Carbon Nitrogen  Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon  Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel  Copper Zinc  Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium  Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Cesium Barium Lanthanum  Cerium Praseodymium  Neodymium Promethium Samarium Europium Gadolinium  Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold  Mercury Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium  Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium  Roentgenium Ununbium Ununtrium Ununquadium Ununpentium Ununhexium Ununseptium Ununoctium	H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 19 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118	1 4 7 9 11 12 14 16 19 20 23 24 27 28 31 32 35 40 30 40 45 48 51 52 55 56 58 58 64 65 70 73 75 79 80 84 85 88 89 91 93 96 98 101 103 106 108 112 115 119 122 128 127 131 133 137 139 140 141 144 145 150 152 157 159 163 165 167 169 173 175 178 181 184 186 190 192 195 197 201 204 207 209 209 210 222 223 226 227 232 231 238 237 244 243 247 247 251 252 257 258 259 262 261 268 263 264 269 268 272 273 277 286 289 288 292 292 293	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118	0 2 4 5 6 6 7 8 10 10 12 12 14 14 16 16 18 22 21 20 24 26 28 28 30 30 31 30 35 35 39 41 42 45 45 48 48 50 50 51 52 54 55 57 58 60 61 64 66 69 71 76 74 77 78 81 82 82 82 84 84 88 89 93 94 97 98 99 100 103 104 106 108 110 111 114 115 117 118 121 123 125 126 125 125 136 136 138 138 142 140 146 144 150 148 151 150 153 153 157 157 157 159 157 N/A 157 157 161 159 162 162 165 173 175 173 176 175 175
Name of Element (Alphabeticallist)	Symbol of Element	Number of Protons Electrons	Mass Number	Atomic Number	Number of Neutrons

Numerical list of Atomic Numbers of Elements