Ch 6 Section 2 Flashcards
A molecule is a neutral group of
Atoms that are held together by covalent bonds
A single molecule of a chemical compound is an individual unit capable of
Existing on its own
Molecules may consist of two or more
Atoms of the same element or two or more different atoms
Molecular compound is a chemical compound whose
Simplest units are molecules
The composition of a compound is given by
It’s chemical formula
A chemical formula indicated the relative numbers of
Atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts
The chemical compound of a molecular compound is referred to as a
Molecular formula
A molecular formula shows the types and numbers of
Atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts
The molecular formula for water reflects the fact that a single water molecule consists of
One oxygen atom joined by separate covalent bonds to two hydrogen atoms
A molecule of oxygen O2 is an example of
A diatomic molecule
A diatomic molecule is a molecule containing
Only 2 atoms
The approaching nuclei and electrons are
Attracted to each other
The attraction between nuclei and electrons corresponds to a decrease in
The total potential energy of the atoms
The two nuclei repel each other and the two electrons
Repel each other which results in an increase in Potential energy
Relative strength of attraction and repulsion between the charged particles depends on the
Distance separating the atoms
When the atoms first sense each other the electron proton attraction is stronger than the
Electron electron and proton proton repulsions
The atoms are drawn to each other and their
Potential energy is lowered
The attractive force continues to dominate and the total potential energy continues to
Decrease until a distance is reached at which the repulsion between the like charges equals the attraction of the opposite charges
When a distance is reached at which the repulsion between like charges equals the attraction of the opposite charges the potential energy is at a
Minimum and a stable hydrogen molecule forms (in the case of a hydrogen-hydrogen bond)
A closer approach of the atoms results in a sharp rise in potential energy as
Repulsion becomes increasingly greater than attraction
The bottom of the valley in the curve represents the
Balance between attraction and repulsion in a stable covalent bond
The molecules electrons can be pictured as
Occupying overlapping orbitals moving about freely in either orbital
The bonded atoms vibrate a bit but as long as their potential energy remains close to the minimum they are
Covalently bonded to each other
The distance between two bonded atoms at their minimum potential energy is the
Bond length
In forming a covalent bond the hydrogen atoms release energy as they
Change from isolated individual atoms to parts of a molecule
The amount of energy released equals the difference between the
Potential energy at the zero level (separated atoms) and that at the bottom valley (bonded atoms)
The same amount of energy must be added to separate the
Bonded atoms
Bond energy is the energy required to
Break a chemical bond and form neutral isolated atoms
Scientists usually report bond energies in kilojoules per mole (kJ/mol) which indicates the
Energy required to break one mile of bonds in isolated molecules
Bond lengths and bond energies vary with the types of
Atoms that have combined
Even the energy of a bond between the same two types of atoms
Varies somewhat depending on what other bonds the atoms have formed
All individual hydrogen atoms contain a single unpaired electron in a
1s atomic orbital
When two hydrogen atoms form a molecule they share
Electrons in a covalent bond
Sharing electrons for hydrogen atoms allows each atom to have
The stable electron configuration of helium
The tendency for atoms to achieve noble gas configurations my bonding covalently extends beyond the
Simple case of a hydrogen molecule
Unlike other atoms the noble gas atoms exist
Independently in nature
Noble gas atoms possess a minimum of energy existing on their own because of the
Special stability of their electron configurations
Other main group atoms can effectively fill their outermost s and p orbitals with electrons by
Sharing electrons through covalent bonding
Such bond formation follows the
Octet rule
Octet rule: chemical compounds tend to form so that each atom by gaining losing or sharing electrons has an
Octet of electrons in its highest occupied energy level
Most main group elements tend to form covalent bonds according to the
Octet rule
Because electron pairs are shared in covalent bonds boron tends to form bonds in which
It is surrounded by six electrons
Other elements can be surrounded by more than with electrons when they
Combine with the highly electronegative elements fluorine, oxygen, and chlorine
In these cases of expanded valence bonding involves electrons in
D orbitals as well as in s and p orbitals
Covalent bond formation usually involves only the electrons in an atoms
Outermost energy levels, the atoms valence electrons
Electron for notation is an electron configuration notation in which
Only the valence electrons of an atom of a particular element are shown indicates by dots places around the elements symbol
In electron dot notation the inner shell electrons
Are not shown
In general an elements number of valence electrons can be determined by adding the
Superscripted of the elements noble gas notation
The pair of dots between the two symbols represents the
Shared pair of a covalent bond
An unpaired pair (lone pair) is a pair of electrons that is not
Involved in bonding and that belongs exclusively to one atom
The pair of dots representing a shared pair of electrons in a covalent bond is often replaced by a
Long dash
Lewis structures: formulas in which atomic symbols represent
Nuclei and inner shell electrons, for pairs or dashes between two atomic symbols represent electron pairs in covalent bonds, and dots adjacent to only one atomic symbols represent unshared electrons
It is common to write Lewis structures that show only the
Electrons that are shared, using dashes to represent the bonds
A structural formula indicated the
Kind number arrangement and bonds but not the unshared pairs of the atoms in a molecule
The Lewis structures for many molecules can be drawn if one knows the
Composition of the molecule and which atoms are bonded to each other
A single covalent bond (single bond) is a covalent bond in which
One pair of electrons is shared between 2 atoms
Atoms of some elements can share
More than one electron pair
A double covalent.bond (double bond) is a covalent bond in which
2 pairs of electrons are shared between 2 atoms
A double bind is shown either by two
Side by side pairs of dots or by two parallel dashes
All four electrons in a double bond belong to
Both atoms
A triple bond is a covalent bond in which
3 pairs of electrons are shared between two atoms
Multiple bonds
Double and triple bonds
Double bonds in general have greater
Bond energies and are shorter than single bonds
Triple bonds are even
Stronger and shorter
In writing Lewis structures for molecules that contain carbon nitrogen or oxygen one must remember that
Multiple bonds between pairs of these atoms are possible
A hydrogen atom always forms a
Single covalent bond
The need for a multiple bond becomes obvious if there are not enough
Valence electrons to complete octets by adding unshared electrons
Some molecules and ions cannot be represented
Adequately by a single Lewis structure
Resonance refers to bonding in
Molecules or ions that cannot be correctly represented by a single Lewis structure
To indicate resonance a double headed arrow is
Placed between a molecules resonance structures
There are many covalently bonded compounds that do not contain individual molecules but instead can be pictures as
Continuous 3 dimensional networks of bonded atoms
Many chemical compounds including most of the chemicals that are in living things and are produced by living things are composed of
Molecules
