Download Atoms: The Building Blocks of Matter

Warm up 9/14/15
• Draw a detailed picture of an
atom. (Think about what you
may have learned in middle
school. What makes up an
atom?)
Atoms: The Building
Blocks of Matter
Chapter 3
Atoms, Compounds &
Molecules
• Atoms: the smallest particle of an element that retains
the chemical properties of that element.
• Compound: a substance that consists of two or more
different types of elements.
• Molecule: a substance that consists of two or more
atoms.
• Ion: An atom or molecule with a net electric charge
due to the loss or gain of electrons.
Dalton: Basic Atomic
Theory
1.All matter
is made of
atoms.
2. Atoms of one element differ in
properties (size, mass etc…) from
atoms of another element.
3. Atoms of different elements
combine in simple, whole-number
ratios to form molecules.
4. In chemical reactions atoms can
combine, separate and rearrange, but not
destroyed.
Structure of the
Atom
• Atoms consist of two regions:
1.Nucleus: Which is a very small
region located in the center of
an atom which contain
positively (+) charged particles
called protons and one or more
(=) neutral particles called
neutrons.
2.Electron cloud: A region very
large compared to the nucleus
which contains very small
negatively (-) charged particles
called electrons.
Structure of the
Atom
• Neutrons, protons and
electrons are called the
subatomic particles.
• Electrons are much
smaller in size and
mass than neutrons
and protons.
Discovery of the
Electron
• Cathode-ray tube experiments performed by JJ
Thompson provided evidence that all atoms contained
negatively charged particles.
Questions raised by the discovery
of the electron
• If it is true that all atoms have these super tiny
negatively charged particles two main questions arise:
1. Because atoms are electrically neutral, they must
contain a positive charge to balance out negative
electrons
2. Because electrons have so much less mass than atoms,
atoms must contain other particles that account for
most of their mass.
Discovery of the
Atomic Nucleus
• Rutherford discovered that all atoms have a very small,
dense and positively charged nucleus by performing what
we call the “gold foil experiment.”
Rutherford’s
Conclusions
• Most of the mass and all of the positive charge of the
atom is in a very dense nucleus.
• However the nucleus only takes up a very small space
in an atom.
• Atoms are mostly empty space.
EXAMPLE: If the nucleus of an atom was the size of a
marble, the size of the atom would be equal to a
football field.
Atomic Number
• Atomic Number: (Z) tells you how many protons are in
each atom of an element. The atomic # identifies the
element.
• Chemical (Atomic) Symbol: Is the letter abbreviation for an
element.
Atomic Number = 6
Chemical Symbol
Examples!
• How many protons are in each of the following:
From yesterday…
• Which 2 subatomic particles did we say
are the biggest/ make up most of an
atom’s mass?
Mass Number
• Mass Number: (A) is the total number of protons and neutrons
that make up the nucleus of an atom.
• Mass Number (A) – Atomic Number (Z) = Number of Neutrons
Mass Number can be written two ways:
Be Able to Interpret
With your group…
• Can the atomic number ever be bigger
than the mass number? Why or why not?
Example!
• How many protons, neutrons, and electrons
are in Carbon 14?
Warm Up 9/21/15
• Why are isotopes important?
isotopes
• Isotopes: are atoms of the same element that have
different masses.
• Isotopes of a particular element all have the same
number of protons and electrons, but different numbers
of neutrons.
Reading Isotopes
Average Atomic Mass
• Although isotopes have different masses, they do not
differ significantly in their chemical behavior.
• Average atomic mass: the weighted average of the
atomic masses of the naturally occurring isotopes of
an element.
• Basically two things matter: the mass and relative
abundance of an elements isotopes.
Nitrogen
• A sample of nitrogen is
tested and has a two
isotopes of nitrogen.
99.64% of atoms are N14 and 0.36% atoms are
N-15. What is the
average atomic mass?
ions
• An ion is an atom or a molecule in which the total
number of electrons IS NOT EQUAL to the number
of protons. This gives the atom or molecule a net
positive or negative ELECTRICAL CHARGE.
CATION
• If a neutral atom loses one or more electrons, it has a
net POSITIVE charge, and is called a CATION.
anion
• If an atom gains electrons, it has a net NEGATIVE
charge and is called an ANION.
Who Cares?
• A lithium-ion battery is a rechargeable battery used in
lots of cell phones and cameras. Lithium ions move
from the negative electrode to the positive electrode
during discharge and back when charging.