Chapter 1
Structure and Bonding: The Periodic Table and Atom Properties
Atomic Structure Isotopes
Isotopes are two atoms of the same
The nucleus contains positively element having a different number of
charged protons and uncharged neutrons.
neutrons.
The electron cloud is composed of Atomic Orbitals
negatively charged electrons. An s orbital has a sphere of
The atomic number is the number of electron density and is lower in
protons in the nucleus and also the energy than the other orbitals of
number of electrons surrounding (i.e. the same shell.
protons = electrons). A p orbital has a dumbbell shape
and contains a node (no electron
The atomic mass is the number of density) at the nucleus. It is
protons plus neutrons in the nucleus higher in energy than the s
12 orbital.
(eg. C has six protons and six
6
neutrons).
Carbon’s atomic number is 6; its
atomic mass 12.
In a neutral atom, the number of
protons equals the number of
electrons.
The Periodic Table
Ions Elements in the same row are
In addition to neutral atoms, atoms can exist similar in size.
as ions Elements in the same column
have similar electronic and
A cation is positively charged and chemical properties.
has fewer electrons than its neutral
form.
An anion is negatively charged and
has more electrons than the neutral
form.
, Bonding
Bonding is the joining of two
atoms in a stable arrangement.
Through bonding, atoms attain a
complete outer shell of valence
electrons (stable noble gas
configuration).
Atoms can form either ionic or
covalent bonds to attain a
complete outer shell (octet rule
for second row elements).
The First Row - Ionic bonds result from the
transfer of electrons from one
element to another.
- Covalent bonds result from
the sharing of electrons
There is only one orbital in the first
between two nuclei.
shell.
Each shell can hold a maximum of
two electrons. Ionic Bonding
Therefore, there are two elements in
the first row: H and He.
The Second Row
Each element in the second row of the An ionic bond generally occurs when
periodic table has four orbitals available to elements on the far-left side of the
accept additional electrons: one 2s orbital periodic table combine with
and three 2p orbitals. elements on the far-right side,
ignoring noble gases.
A positively charged cation formed
from the element on the left side
attracts a negatively charged anion
formed from the element on the right
side (eg. Sodium chloride, NaCl).
Each of the four orbitals in the
Li loses its one electron to make Li+
second shell holds two electrons.
which has no electrons in second
There is a maximum capacity of
shell. However, it has a complete
eight valence electrons for elements
first shell.
in the second row.
F gains one electron to make F-
The second row of the periodic table
which has a filled valence shell (an
consists of eight elements, obtained
octet of electrons like neon (Ne).
by adding electrons to the 2s and
three 2p orbitals.
, Valence Electrons
Second-row elements can have no
more than eight electrons around
them. For neutral molecules, this
has two consequences:
- Atoms with one, two, three, or
four valence electrons form one,
two, three, or four bonds,
Covalent Bonding respectively, in neutral
molecules. (e.g., BF , CH ).
3 4
Covalent bonding occurs with
elements like carbon in the middle of
- Atoms with five or more valence
the table (eg. CH ) with elements electrons form enough bonds to
4 give an octet (e.g., NH ). Thus,
that have similar electronegativity. 3
results to the equation above.
Covalent bonds also occur between
two of the same elements from the
same sides of the table (eg. H , Cl ). Nonbonded Electrons
2 2
When second-row elements form
A covalent bond is a two-electron fewer than four bonds, their octets
bond, and a compound with covalent consist of both bonding (shared) and
bonds is called a molecule. nonbonding (unshared) electrons.
Unshared electrons are also called
Bonding in Molecular Hydrogen (H ) lone pairs.
2
Hydrogen forms one covalent
bond.
When two hydrogen atoms are
joined in a bond, each has a
filled valence shell of two
electrons.
Lewis Structures
Lewis structures are electron dot
representations for molecules.
Structure and Bonding: The Periodic Table and Atom Properties
Atomic Structure Isotopes
Isotopes are two atoms of the same
The nucleus contains positively element having a different number of
charged protons and uncharged neutrons.
neutrons.
The electron cloud is composed of Atomic Orbitals
negatively charged electrons. An s orbital has a sphere of
The atomic number is the number of electron density and is lower in
protons in the nucleus and also the energy than the other orbitals of
number of electrons surrounding (i.e. the same shell.
protons = electrons). A p orbital has a dumbbell shape
and contains a node (no electron
The atomic mass is the number of density) at the nucleus. It is
protons plus neutrons in the nucleus higher in energy than the s
12 orbital.
(eg. C has six protons and six
6
neutrons).
Carbon’s atomic number is 6; its
atomic mass 12.
In a neutral atom, the number of
protons equals the number of
electrons.
The Periodic Table
Ions Elements in the same row are
In addition to neutral atoms, atoms can exist similar in size.
as ions Elements in the same column
have similar electronic and
A cation is positively charged and chemical properties.
has fewer electrons than its neutral
form.
An anion is negatively charged and
has more electrons than the neutral
form.
, Bonding
Bonding is the joining of two
atoms in a stable arrangement.
Through bonding, atoms attain a
complete outer shell of valence
electrons (stable noble gas
configuration).
Atoms can form either ionic or
covalent bonds to attain a
complete outer shell (octet rule
for second row elements).
The First Row - Ionic bonds result from the
transfer of electrons from one
element to another.
- Covalent bonds result from
the sharing of electrons
There is only one orbital in the first
between two nuclei.
shell.
Each shell can hold a maximum of
two electrons. Ionic Bonding
Therefore, there are two elements in
the first row: H and He.
The Second Row
Each element in the second row of the An ionic bond generally occurs when
periodic table has four orbitals available to elements on the far-left side of the
accept additional electrons: one 2s orbital periodic table combine with
and three 2p orbitals. elements on the far-right side,
ignoring noble gases.
A positively charged cation formed
from the element on the left side
attracts a negatively charged anion
formed from the element on the right
side (eg. Sodium chloride, NaCl).
Each of the four orbitals in the
Li loses its one electron to make Li+
second shell holds two electrons.
which has no electrons in second
There is a maximum capacity of
shell. However, it has a complete
eight valence electrons for elements
first shell.
in the second row.
F gains one electron to make F-
The second row of the periodic table
which has a filled valence shell (an
consists of eight elements, obtained
octet of electrons like neon (Ne).
by adding electrons to the 2s and
three 2p orbitals.
, Valence Electrons
Second-row elements can have no
more than eight electrons around
them. For neutral molecules, this
has two consequences:
- Atoms with one, two, three, or
four valence electrons form one,
two, three, or four bonds,
Covalent Bonding respectively, in neutral
molecules. (e.g., BF , CH ).
3 4
Covalent bonding occurs with
elements like carbon in the middle of
- Atoms with five or more valence
the table (eg. CH ) with elements electrons form enough bonds to
4 give an octet (e.g., NH ). Thus,
that have similar electronegativity. 3
results to the equation above.
Covalent bonds also occur between
two of the same elements from the
same sides of the table (eg. H , Cl ). Nonbonded Electrons
2 2
When second-row elements form
A covalent bond is a two-electron fewer than four bonds, their octets
bond, and a compound with covalent consist of both bonding (shared) and
bonds is called a molecule. nonbonding (unshared) electrons.
Unshared electrons are also called
Bonding in Molecular Hydrogen (H ) lone pairs.
2
Hydrogen forms one covalent
bond.
When two hydrogen atoms are
joined in a bond, each has a
filled valence shell of two
electrons.
Lewis Structures
Lewis structures are electron dot
representations for molecules.
