Need help on an exam on Chemistry
njm.500
Chapter2.pdf
1/17/2018
1
N'vida E. Houndonougbo
Chapter 2: Atoms Learning objectives
• Sketch the nuclear model of the atom, and identify its parts (3.4)
• List the particles that make up the nucleus of an atom, and give
their relative masses and electric charges. (3.5)
• Identify elements and isotopes from their nuclear particles. (3.5)
• Describe what a mole is and how it is used.
• Convert between the masses and the moles of a substance
N'vida E. Houndonougbo
Chapter 2
Suggested Assignment:
• Page 76: Self-assessment questions
• Page 91: Review questions 11; 16 a, b, c, e; 17
• Page 91: problems 22 to 28
• Page 160: problem 27 to 28
1/17/2018
2
N'vida E. Houndonougbo
Chapter 2:
Outline
I. Atoms and their components
II. Isotopes
III. Mole and Avogadro’s number
IV. Molar Mass
N'vida E. Houndonougbo
The Components of Atoms
Atoms can be broken up into simpler components
by the application of large amounts of energy.
Two types of components are formed: a nucleus
and electrons
1/17/2018
3
N'vida E. Houndonougbo
The Components of Atoms
The nucleus of an atom contains protons and neutrons.
• A proton carries a positive electrical charged (+ 1) and has a mass
approximately 1 amu.
1 amu = 1.6605 x 10-24 g
• A neutron has no electric charge (0) and has a mass approximately
1 amu
Electrons have a very small mass (5 x 10-4 amu) and carry a small
negative electrical charge (- 1) . Electrons have approximately 1/1800
times the mass of an proton.
Atoms are composed of tiny subatomic particles called: protons,
neutrons, and electrons.
Because every atom has the same amounts of negative and positive
electrical charge, atoms are electrically neutral
N'vida E. Houndonougbo
The nuclear model of Atoms Rutherford’s experiments led to the
nuclear model of the atom.
The modern concept of the atom is
that:
• Atom is a sphere consisting mostly of
empty space.
• Atom contains a tiny dense nucleus
which lies at the center of the sphere.
Its diameter is approximately 10-15 m.
• The electrons travel at extremely high
speeds around the nucleus .
1/17/2018
4
N'vida E. Houndonougbo
The atomic number
.Each element has a
characteristic number of protons
in the nucleus, called atomic
number.
The atomic number of an
element distinguishes that
element from another.
Atomic number (Z): The
number of protons in the nucleus
of an atom.
Practice: in class
N'vida E. Houndonougbo
Isotopes In nature, most elements consist of mixture of isotopes.
Isotopes are atoms of the same element with different mass
number =( The sum of the number of protons and neutrons
in the nucleus of an atom)
Hydrogen exists in nature as one of 3 isotopes:
• 1H (99.98%) hydrogen or Hydrogen-1
• 2H (0.02%) deuterium or Hydrogen-2
• 3H (rare) tritium or Hydrogen-3
1/17/2018
5
N'vida E. Houndonougbo
Isotopes and Atomic Weight
Atomic weight or atomic mass: Weighted average of the
masses (in amu) of the naturally occurring isotopes of an
element.
Memorize!!! Atomic weight = (isotope abundance)*(isotope mass)
Example:
9
N'vida E. Houndonougbo
The Mole and Avogadro’s number
• The unit used to count the huge number
of atoms or molecules in a sample is
called the mole.
• A mole (mol) is defined as the amount of
a substance that contains 6.02 × 1023
particles.
• 6.02 × 1023 Is known as Avogadro’s number.
• This is the same relationship as the term
dozen is to 12.
1/17/2018
6
N'vida E. Houndonougbo
Molar Mass
The mass, in grams of one mole of a substance is
known as the molar mass (MM) of that substance.
The molar mass of a compound is the sum of the
atomic masses of the elements in that compound.
(g/mol).
Example: in class
N'vida E. Houndonougbo
The Mole and Avogadro’s Number
We can use the mole relationship to convert between the
number of particles and the number of mole.
Chemists and chemical engineers must perform calculations
based on chemical reactions to predict the cost of processes.
Calculations are used to avoid using large, excess amounts of
costly chemicals.
