Topic 3 Bonding and Structure Flashcards
What is ionic Bonding
Electrostatic attraction between oppositely charged ions arranged in a lattice
Why are ions of the same charge not repulsed in the ionic compound
Electrostatic attraction between oppositely charged ions is greater than electrostatic repulsion between ions of the same charge
How can we calculate the strength of an ionic bond
By calculating the amount of energy required in mole of solid to separate the ions to infinity (i.e. in the gas phase). When they are at an infinite distance from each other, the ions can no longer interact
What affects the strength of an ionic bond
1) The size of the ions
2) The charge on the ions
How does the size of the ion affect the ionic bond
The smaller the ion, the more energy is needed to overcome the electrostatic interactions between the ions and separate them, hence a stronger ionic bond
How does the charge of the ions effect the strength of the ionic bond
The greater the charge, the greater the ionic bond
Provide evidence for the existence of ions
1) electron density maps
2) molten and aqueous compounds can conduct electricity and undergo electrolysis
What does isoelectronic mean
ions with the same number of electrons and therefore the same electron configuration
How does ionic radii vary as you move down a group
ionic radii increases as the ions have more electron shells; therefore, the ions get larger
What causes different ionic radii between isoelectric ions
Different numbers of protons lead to different atomic radii. As the positive charge of the nucleus increases, the electrons are attracted more strongly and are pulled closer to the nucleus
What is polarization
the distortion of the electron density of a negative ion (anion)
this occurs when a positive ion attracts the electrons of an anion
What is polarizing power
the ability of a positive ion to distort the electron density of a neighboring negative ion
What are the two ways Fajan’s rule states polarization POWER can be increased by
1) high charge and small size of cation (i.e. high density of the cation)
2) high charge and large size of anion
Which cations have the larges polarizing power
high charge and small radius (as a result of small size)
How can polarizing power of a cation be calculated
by calculating the charge density, which is calculated by charge/surface area
if the ion is a sphere, surface area can be calculated by 4 x pie x r^2 (where r is the ionic radius)
an approximation of the charge density can be calculated by diving charge by the square of ionic radius
Typical properties of ionic compounds
high m.p
brittle
poor electrical conductor when solid, but good conductor when molten or aqueous
soluble in water
why do ionic compounds have high melting points
The electrostatic forces of attraction between the ions are relatively strong and hence a large
amount of energy is required to overcome them and allow the ions to break free from the
lattice structure and slide past one another.
why are ionic compounds brittle
if enough force is applied, the layers of ions may slide over each other. With ions of the same charge now side by side, the ions repel each other and the crystal breaks
Why cant solid ionic compounds conduct electricity
because there are no delocalized electrons and ions are not free to move under the influence of an applied potential difference
Why can molten ionic compounds conduct electricity
ions are mobile and will migrate to the electrodes of opposite sign when a p.d is applied
why can aqueous ionic compounds conduct electricity
compound breaks down into separate ions when the compound dissolves
Why can ionic compounds dissolve
energy required to break apart the lattice structure and separate the ions can be supplied by the ions produced. Positive and negative ions are attracted to water molecules because of the polarity that water molecules possess
What are covalent bonds
electrostatic attraction between the two nuclei of the bonded atoms and the pair of electrons shared between them
What are the ways in which orbitals may overlap
1) sigma bond-end on overlap of two s-orbitals
2) sigma bond- end on overlap of two p-orbitals
3) pi bond- sideways overlap of two p-orbitals
what is a sigma bond
end on overlap of s-orbitals or p-orbitals leading to the formation of a single covalent bond between the two atoms
what is a pi-bond
sideways overlap of two p-orbitals leading to the formation of double or triple bonds. A pi bond cant form until an alpha bond has been formed.
What determines the strength of a covalent bond
the amount of energy required to break one mole of the bond in the gaseous state
Explain the relationship between between bond length and bond strength
the shorter the bond, the greater the bond strength. this is a result of an increase in electrostatic attraction between the two nuclei and the electrons in the overlapping atomic orbitals
What is electronegativity
the ability of an atom to attract a bonding pair of electrons in a covalent bond
What are the electronegativity across a period and down a group
1) decreases down a group
2) increases from left to right across a period
What is bond length
the distance between the nuclei of two atoms that are covalently bonded together
What is the distribution of the electron density when two atoms of the same element are covalently bonded together
the electron distribution between the two nuclei will be symmetrical because the ability of each atom to attract the bonding pair of electrons is identical
what is a polar covalent bond
a type of covalent bond where the bonding electrons are unequally distributed; because of this, one atom carries a slight negative charge and the other a slight positive charge
how do polar covalent bonds form
when two atoms are bonded together that are from elements that have different electronegativities. The distribution of electron density will not be symmetrical about the two nuclei.
what symbols are used to represent a slightly positive and slightly negative charge in a molecule with a polar covalent bond
S+ and S-
what symbols are used to represent a slightly positive and slightly negative charge in a molecule with a polar covalent bond
S+ and S-
What is a discrete (simple) molecule
an electrically neutral group of two or more atoms held together by covalent bonds
What is the octet rule
In order to form a stable compound, the outer shell of an atom must have the same amount of electrons as the outer shell of a noble gas.
however, this is not always true
What is a displayed formula
shows a bonding pair by usig lines
for example: O=O
H-O-H
What is a dative covalent bond
the bond formed when an empty orbital of one atom overlaps with an orbital containing a lone pair of electrons of another atom
In the displayed formula with dative bonding, where does the arrow point?
From the atom providing the pair of electrons to the atom with the empty orbital (the atom that is electron deficient)
What is a dipole
it is the separation of charge and it exists when two charges of equal magnitude but opposite sides are separated by small distances
Why is there a separation of charge
bonded electrons drift towards the more electronegative element
When is a molecule non-polar
when the molecule has no overall dipole and the cancelation is complete
When is a molecule polar
when the dipoles reinforce one another
Where does the dipole symbol point
towards the more electronegative element
