Download Atoms: The Building Blocks of Matter

Atoms: The Building Blocks of
Matter
Chapter 3
Basic laws of chemical
reactions

Law of conservation of mass: mass is
neither created nor destroyed in ordinary
reactions

Law of definite proportions: a chemical
compound always contains the same
elements in exactly the same proportions by
mass regardless of the size of the sample or
the source of the compound
Dalton’s Atomic Theory
1.
2.
3.
4.
5.
All matter is composed of extremely small
particles called atoms.
Atoms of a given element are identical in size,
mass, & other properties.
Atoms cannot be subdivided, created, or
destroyed.
Atoms of different elements combine in simple
whole number ratios to form chemical
compounds.
In chemical reactions, atoms are combined,
separated, & rearranged.
The modern atomic theory has
proven that atoms are divisible into
smaller particles & that a given
element can have atoms with
different masses.
The Atom

Atom: smallest particle of an element that
retains the chemical properties of that
element

Contains 2 parts:
 Nucleus: located near the center of the
atoms
 Electron cloud: located in rings around
the nucleus
Subatomic Particles

The atom contains 3 basic subatomic
particles:



Proton: positively charged particle
located inside the nucleus
Neutron: neutrally charged particle
located inside the nucleus
Electron: negatively charged particle
located in the rings of the electron cloud
Atomic & Mass Number

atomic number (Z): number
of protons in the nucleus of
each atom
The atomic number identifies
an element.

mass number: total number
of protons & neutrons in the
nucleus
Scientists use atomic mass
units (amu) to measure the
mass of atoms.
Isotopes


All atoms are composed of the same basic
particles, but all atoms are not the same.
Atoms of different elements have different
number of protons.
Isotope: atoms of the same element that
have different masses
Cont’d…

Most elements occur naturally as a
mixture of isotopes.

Average atomic mass: weighted
average of the atomic masses of the
naturally occurring isotopes of an
element
Problem
Copper is a naturally occurring
isotope. It consists of 69.17%
copper-63 and 30.83% copper-65.
Calculate the average atomic
mass of the naturally occurring
copper if copper-63 weighs
62.929598 amu and copper-65
weighs 64.927793 amu.
The Mole

Mol: SI unit for amount of substance

Avogadro’s number: number of particles
in a mole, 6.02x1023

Molar mass: mass of 1 mole of a pure
substance


Written in grams/mole (g/mol)
Equal to the atomic mass number found on
the periodic table
Mole Conversions
Problems
1.
2.
3.
4.
What is the mass in grams of 3.50 mol of
the element copper?
A chemist produced 11.9 g of aluminum.
How many moles of aluminum were
produced?
How many moles of silver (Ag) are in
3.01x1023 atoms of Ag?
What is the mass in grams of 1.20x108
atoms of copper?