S1-L7: Ionic Bonding 1 Flashcards
What are “chemical bonds”?
- attractive forces which holds 2+ atoms together in molecule
- ->involves valence e-‘s (most available)
Explain how atoms combine to gain stability
- e-‘s in atoms distribute themselves in orbitals in most stable/lowest e- configuration
- re-arranging e-‘s between atoms–> allows combined molecules to achieve even lower energy
What is the “Octet rule”?
-all elements (except Nobel gases) show tendency yo join with other elements to form compounds
How do elements achieve the Octet structure?
- atoms tend to adjust their valence shell 8 e- by losing/gaining/sharing e-
- ->so have same e- configuration as Nobel gas
To which group of elements does the Octet rule apply to?
- applies to main group of elements BUT some exceptions
- ->notably transition metals using d-orbitals obey 18e- rule instead
Outline what forces between atoms are
- attractive + repulsive forces operate between 2 atoms when they come close to each other
- ->like charges repel (e-/e-) AND nucleus/nucleus (+)
How does bond length affect interaction?
- refer to figure 1
- as increases interaction energy decreases (stable) up to optimum point when distance then starts closing up and consequently interaction energy increases towards unstable point
Define “electronegativity”
-ability of atom to attract towards itself the e-‘s in a chemical bond
What factors affect electronegativity?-Explain where appropriate
- n. of protons in nucleus
- distance from nucleus/atom size
- ->smaller ones able to approach nucleus more closer
- amount of screening by inner e-‘s
- ->i.e: n. of full shells between valence shells AND nucleus
- covalent bond–>polarity of bonds
- ionic bonds–>initial transfer of e-‘s
Which element is the most electronegative and why?
- Fluorine
- ->because small AND has high nuclear charge
1-Electronegativity of elements: Pauling scale
2-Types of bonds
3-Electronegativity and bonding
1-Figure 2
2-Figure 3
3-Figure 4
Explain what ionic bonding is
- ionic bonds formed when one or more e-‘s fully transferred between atoms
- ionic bonding takes place between metals AND non-metals
- non-metals try to reach + maintain noble gas structure via gaining e-‘s to form (-) ions (anions)
- (+) and (-) ions attract via electrostatic attraction t ogive ionic bond
- ionic bond formation involves energy decrease compared to the 2 isolated atoms
Formation of an Ionic Bond
-refer to figure 5
What is the significance of e- change to achieve a full outer shell
- change in e-‘s must be minimum
- ->i.e: lose 2 not gain 6
What happens as e- are lost and gained?
- gain 1 (+) charge for each e- lost
- gain 1 (-) charge for each e- gained
- valency of ion equals its charge
Define the term “isoelectronic”
-having same n. of e-‘s/electronic structure
Outline the key properties of Ionic Bonds
- ionic bond formed due to electrostatic attraction between (+) AND (-) charged ions
- non-directional bond–> strength of interaction between two ions depends on distance BUT not on direction
- ionic compounds easily dissolve + dissociate in polar solvents (i.e: water)–>bond broken–>ions separated (ion + solvent strongly attracted)
- bonds also break when substance melted
- ionic compound not charged overall
What are the features of an ionic bond?
- formed between metals + non-metals
- dissolve easily in water AND other polar solvents
- conduct electricity when molten AND in solution
- form crystalline solids with high melting temps
Describe the “ionic lattice” (figure 6)
- every ion attracted to all other ions with opposite charge
- ->results in repeating 3D pattern on anions (-) AND cations (+) in solid state
- giant structure
What is “Lattice Energy”?
-enthalpy of formation (energy change) of forming 1 mole of ionic solid from it’s gaseous ions
–>measures bond strength
-E.G: Na+ (g) + Cl- (g) –>NaCl (s)
(-786 kj/mol)
How does easy cation (+) and easy anion (-) formation favour ionic bonding?
- Cation (+): low ionisation energy of metal
- Anion (-): high e- affinity/ electronegativity of non-metal
What other factors favour ionic bonding?
- small size of non-metal
- low charge on anion
- large electronegativity difference between the combining atoms
- high lattice energy of compound
Define the term “polarisation”
-distortion of e- cloud of atom
What is polarising power?
-ability to distort electron cloud of another atom
State the factors which increase the polarising power
- smaller ion + higher it’s charge
- larger atom AND more e-‘s has
Comparison of atoms before form ions and size of ionj formed
-Refer to figure 7 to see comparison
How do cations and anions compare in terms of polarisation?
- cations typically smaller than anions
- ->so tend to have more polarising power while anions tend to be more polarisable (have e- cloud distorted)
What does Fajan’s rule state about the type of character an atom has?
- negative ion distorted–>covalent character
- no polarisation–> ideal ionic compound
Describe an “Ideal Ionic Compound” (figure 8)
- composes of completely separate spherical ions
- ->polarisation results in non-spherical ions AND covalent character in bond
What does Fajan’s rule state about the covalent character an ionic compound may have?
- cation small AND OR high charge–>highly polarising
- anion large AND OR high charge–>highly polarising
Example: Why does LiCl have a low m. point and is hydrolysed by water?
- Li+ small with high charge density
- Cl- large with it’s e-‘s far from nucleus
Outline and describe “Polyatomic Ions”
- Ions made up of more than one type of atom
- bonding within polyatomic atoms covalent
- n. of e-‘s means group has overall charge–>so able to make ionic bonds
Common polyatomic ions
-Ammonium (NH4+)/ Cyanide (CN-)/ Hydroxide (OH-)/ Peroxide (O2^2-)/ Acetate (CH3CO2-)/ Oxalate (C2O4^2-)/ Nitrate (NO3-)/ Sulfate (SO4^2-)/ Carbonate (CO3^2-)/ Phosphate (PO4^3-)/ Permanganate (MnO4-)/ Dichromate (Cr2O7^2-)
How is an ionic compound named?
- first word in name cation–>usually same as parent element (except ammonium)
- oxidation state of metal can be given after name–>like copper (II)/Iron (III)
- second word in name is cation
- ->if second ion polyatomic then it is just name of polyatomic ion
- if second ion element is end of element’s name then change to -ide
- ->e.g: Chlorine–>chloride OR oxygen–>oxide
Outline important Cations in the body and the significance of some
- Na+/K+ : signaling/ muscle contraction
- Ca2+ : skeleton–>key role in bones
- H+/ Mg2+
What are some of the important Anions in the body?
-Cl-/ HCO3-/ HPO4 2-/ SO4 2-/ PO4 3-
Summary of lecture
- Chemical bonding: attractive AND repulsive forces between atoms
- lowering of energy of combining atoms
- octet rule
- electronegativity
- Types of chemical bond-Ionic Bond:
- ion formation
- ions & ionic bonds
- ionic bonding AND periodic table
- ionic compound properties
- naming of ionic compounds
