Transcript Atoms and Bonding

Atoms and Bonding
The Building Blocks of Matter
Matter may consist of elements, compounds, or mixtures.
Compound: a
substance made of two or
more elements chemically
bonded together.
Mixture: a physical
combination of two or
more pure substances
(i.e., elements or
compounds).
Element:
a substance made of
only one type of atom
Atoms and Bonding
Atomic Theory and Models
Dalton thought that atoms were like smooth, hard balls that
could not be broken into smaller pieces.
Atoms and Bonding
Atomic Theory and Models
Thomson suggested that atoms had negatively charged
electrons embedded in a positive sphere.
Atoms and Bonding
Atomic Theory and Models
Rutherford was surprised that a few particles were deflected
strongly. This led him to propose an atomic model with a
positively charged nucleus.
Atoms and Bonding
Atomic Theory and Models
Through the first part of the twentieth century, atomic models
continued to change.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
* Valence Electrons: the electron(s) in the outer shell of an atom’s
electron cloud, which can combine with other atoms to form
molecules
*The number of valence electrons in an atom of an element
determines many properties of that element, including the
ways in which the atom can bond with other atoms.
Atoms and Bonding
Atoms and Bonding
The Periodic Table
Elements are organized into rows and columns based on
their atomic number.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
Periodic Table Activity
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the periodic table.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
The Periodic Table
As the number of protons (atomic number) increases, the
number of electrons also increases. As a result, the
properties of the elements change in a regular way across a
period.
Atoms and Bonding - Atoms, Bonding, and the Periodic Table
The Periodic Table
The variety of colors in a “neon” sign
results from passing an electric
current through sealed glass tubes
containing different noble gases.
Atoms and Bonding
Ions and Ionic Bonds
You and a friend walk past a market that sells apples for 40
cents each and pears for 50 cents each. You have 45 cents
and want an apple. Your friend also has 45 cents but wants a
pear.
Atoms and Bonding - Ionic Bonds
Ions and Ionic Bonds
When an atom loses an electron, it loses a negative charge
and become a positive ion. When an atom gains an electron,
it gains a negative charge and becomes a negative ion.
Atoms and Bonding
Graphic Organizer
Polar
Covalent
Bond
Nonpolar
Covalent
Bond
Metallic
Bond
Equal sharing
of electrons
Attraction
between positive
ions and
surrounding
electrons.
Feature
Ionic Bond
How Bond
Forms
Attraction
between
oppositely
charged ions
Unequal sharing
of electrons
Charge on
Bonded
Atoms?
Yes; positive or
negative
Yes, slightly
positive or slightly No
negative
Yes; positive
Example
NaCl crystal (or
other ionic
compound)
H2O molecule (or
other polar
covalent
molecule)
Calcium (or
other metal)
O2 molecule
Atoms and Bonding - Ionic Bonds
Ions and Ionic Bonds
Ions are atoms that have lost or
gained electrons.
Atoms and Bonding - Ionic Bonds
Ionic bonding is the process of two or more atoms losing or
gaining electrons to become charged ions. The charged ions
are then attracted to each other:
Na + Cl -> Na+Cl-
Atoms and Bonding - Ionic Bonds
Properties of Ionic Compounds
In general, ionic compounds are hard, brittle crystals that
have high melting points. When dissolved in water or melted,
they conduct electricity.
Atoms and Bonding - Covalent Bonds
Non-Polar Covalent Bonds: chemical bonding defined as the equal
sharing of electrons by two or more atoms to produce a shared attraction. The
atoms tend to share electrons, so as to fill the outer electron shell, which can
hold up to eight electrons (except for hydrogen and helium, which can
accommodate only 2 electrons in the outer shell).
Atoms and Bonding - Covalent Bonds
How Covalent Bonds Form
An oxygen molecule contains one double bond, while a
carbon dioxide molecule has two double bonds. A nitrogen
molecule contains one triple bond.
Atoms and Bonding - Covalent Bonds
Unequal Sharing of Electrons
Fluorine forms a nonpolar bond with another fluorine atom. In
hydrogen fluoride, fluorine attracts electrons more strongly
than hydrogen does, so the bond formed is polar.
Atoms and Bonding - Covalent Bonds
Unequal Sharing of Electrons
A carbon dioxide molecule is a nonpolar molecule because
of its straight-line shape. In contrast, a water molecule is a
polar molecule because of its bent shape.
Atoms and Bonding - Bonding in Metals
Metallic Bonding
A metal crystal consists of positively
charged metal ions embedded in a
“sea” of valence electrons.
Atoms and Bonding - Bonding in Metals
Metallic Properties
The “sea of electrons”
model of solid metals
explains their ability to
conduct heat and
electricity, the ease with
which they can be made
to change shape, and
their luster.