Topic 2- Bonding And Structure Flashcards
What is ionic bonding
The strong electrostatic attractive between oppositely charged ions
understand the effects that ionic radius and ionic charge have on the strength of ionic bonding
Ionic charge - greater the charge the stronger the ionic bond and higher mp +bp
Ionic radii - smaller ions can pack closer together , attraction get weaker with distance, small ions have a stronger bond higher mp and bp
understand the formation of ions in terms of electron loss or gain
Ions are formed when electrons are transferred from one atom to another , they can be positive (cation) or negative (anion)
be able to draw electronic configuration diagrams of cations and anions using dot-and-cross diagrams
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understand reasons for the trends in ionic radii down a group and for a set of isoelectronic ions, e.g. N3– to Al3+
Down group - radius increases as you go down bcs atomic number increases so more electron shells
Isoelectric ions - radius decreases as atomic number increases, more protons more electrons attracted to nucleus so decrease in radii
understand that the physical properties of ionic compounds and the migration of ions provide evidence for the existence of ions
High mp- ions are held together by strong attraction ( + - ions are attracted fits evidence )
Solvable in water but not in non polar solvents- particles are charged as pulled apart by water (polar) but not non polar substances fits evidence
Don’t conduct when solid- ions are fixed by strong ionic bonds but are free to move as a liquid
Cant be shaped- if moved you’d get to negative ions on top of each other , repulsion would be strong so ionic compounds are brittle, supports the lattice model.
Migration of ions
- when you electrolyse a free solution of copper (ll) chromate (vl) on wet filter paper it ruins blue at the cathode and yellow at the anode
- copper (ll) ions are blue in solution and chromate (vl) are yellow
- when you pass a current the positive ions move to the cathode (blue ) and the negative ions move to the anode (yellow)
What is a covalent bond
The strong electrostatic attraction between two positive nuclei and the shared pair of electrons between them in the bond.
be able to draw dot-and-cross diagrams to show electrons in covalent substances, including:
i molecules with single, double and triple bonds
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understand the relationship between bond lengths and bond strengths for covalent bonds
- the distance between the nuclei is where the attractive and repulsive forces balance each other out , aka bond length
- the higher the electron density between the nuclei the stronger the attraction between the atoms , so higher bond enthalpy and shorter bond length
- more attraction the nuclei are puller closer together.
understand that the shape of a simple molecule or ion is determined by the repulsion between the electron pairs that surround a central atom
- electrons try to repel each other type of electron pair effects how much its repelled, shape depends on type of electron pair surrounding central atom
- Lp Lp > Lp Bp> BpBp
- predicting shape known as ‘electron pair repulsion theory’
be able to predict the shapes of, and bond angles in, simple molecules and ions analogous to those specified above using electron-pair repulsion theory
- find central atom and work out number of electrons in the outer shell
- use the molecular formula to work out how many electrons are shared with the atom
- add up electrons and divide by 2 to work out electron pairs
- compare pairs with bonds to find Lp
- then can work out the shape once you know how many Lp and Bp
understand reasons for the shapes of, and bond angles in, simple molecules and ions with up to six outer pairs of electrons (any combination of bonding pairs and lone pairs)
Examples should include BeCl2, BCl3, CH4, NH3, NH4+, H2O, CO2, PCl5(g) and SF6(g) and related molecules and ions; as well as simple organic molecules in this specification.
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Shapes of molecules
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be able to draw dot-and-cross diagrams to show electrons in covalent substances, including: species exhibiting dative covalent (coordinate) bonding, including Al2Cl6 and ammonium ion
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What is electronegativity
s the ability of an atom to attract the bonding electrons in a covalent bond
know that ionic and covalent bonding are the extremes of a continuum of bonding type and that electronegativity differences lead to bond polarity in bonds and molecules
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understand that molecules with polar bonds may not be polar molecules and be able to predict whether or not a given molecule is likely to be polar
- polar molecules have an overall dipole
- in simple molecules HCl the polar bond gives the molecule a permanent dipole
- more complicated molecules have many polar bonds, if arranged in opposite directions they’ll cancel each other out (non polar) if arranged in the same direction it’s polar.
understand the nature of intermolecular forces resulting from the following interactions:
i London forces (instantaneous dipole – induced dipole)
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understand the nature of intermolecular forces resulting from the following interactions: permanent dipoles
The charges on a polar molecule can cause weak electrostatic attraction between molecules egHcl
They happen as well as London forces , so will have a higher bp and mp than those with simple London forces that can’t form a permanent dipole.
understand the nature of intermolecular forces resulting from the following interactions
hydrogen bonds
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understand the interactions in molecules, such as H2O, liquid NH3 and liquid HF, which give rise to hydrogen bonding
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