topic 2 - bonding and structure Flashcards
what is the definition of a chemical bond
a force of electrostatic attraction between positive nuclei and negative electrons which hold together 2 or more atoms, ions or molecules
what is the definition of valency
the ability for an atom to form bonds
what is the valence shell and valence electrons
valence electrons are electrons that form bonds
the valence shell contains the valence electrons, so its the highest energy outermost shell
what is the definition of an ionic bond
the electrostatic force of attraction between anions and cations
these ions are formed from the loss and gain of electrons
in ionic bonding, what can be said about the force of attraction and repulsion
the ions are arranged in a lattice structure so that that the electrostatic force of attraction between oppositely charged ions is greater than the electrostatic repulsion between ions with the same charge
what can make ionic bonding stronger
-the smaller the ionic radius, the stronger the electrostatic force of attraction between oppositely charged ions, therefore more energy is required to break the ionic bond
-the greater the charges on the ions the stronger the ionic bonding
explain what happens to atomic radius as the number of protons increase
-as proton number increases atomic radius decreases
-because the positive charge of the nucleus will increase, so the electrostatic attraction between the nucleus and electrons increases, so electrons are pulled closer to the nucleus
what are the 5 physical properties of ionic compounds
high melting point
brittleness
poor conductors of electricity when solid
good conductors of electricity when molten or aqueous
soluble in water
explain why ionic compounds have a high melting point
-giant regular lattice structure
-containing electrostatic forces of attraction between anions and cations
-these forces are very strong and need a lot of energy to break
explain why ionic compound are brittle
-when a force is applied to a solid ionic compound the layers of ions slide over eachother
-causing ions of the same charge to be side by side
-they repel each other
-so the solid breaks apart
explain why solid ionic compounds do not conduct electricity
-the ions are not free to move and there are no delocalised electrons
explain why molten or aqueous ionic compounds do conduct electricity
-the ions in the giant regular lattice structure are free to move
-the ions will migrate to the electrode with the opposite charge when a potential difference is supplied
-if direct current is used the ionic compound will undergo electrolysis, causing the ions to be discharged at the electrodes
explain why ionic compounds are soluble
-the energy needed to break apart the lattice structure and separate the ions is supplied by the hydration of separated ions
-the delta negative oxygen in water molecules is attracted to cations in the ionic compound
-delta positive hydrogen in water molecules are attracted to anions in the ionic compound
what are isolecetronic ions
ions which all have the same number of electrons
but can be different elements
why is there variation in ionic radius in a set of isoelectronic ions
–as proton number increases ionic radius decreases
-because the positive charge of the nucleus will increase, so the electrostatic attraction between the nucleus and electrons increases, so electrons are pulled closer to the nucleus
what is 1 piece of evidence for the existence of ions
the ability for an ionic compound to conduct electricity and undergo electrolysis
explain the electrolysis of molten sodium chloride
-positive sodium cations migrate towards the negative cathode, where they gain electrons (reduction), becoming sodium atoms
-negative chlorine anions migrate towards the positive anode, where they lose electrons (oxidation), becoming chlorine atoms
describe how the movement of ions can be demonstrated visually using copper(II) chromate(VI) solution
-aqueous copper(II) ions are blue
-aqueous chromate(VI) ions are yellow
-copper(II) cations migrate towards the cathode, and the solution around the cathode turns blue
-chromate(VI) anions migrate towards the anode, and the solution around the anode turns yellow
how is a sigma bond formed
end on overlap of 2 orbitals which both contain 1 electron only
how is a pi bond formed
sideways overlap of 2 p-orbitals
pi bonds can only form once a sigma bond has formed
so pi bonds only exist between atoms which have double/triple bonds
what type of bond is a single covalent bond between 2 atoms
sigma bond
end on overlap of 2 orbitals
what are the bonds in a triple covalent bond
1 sigma bond
2 pi bonds
what is bond length
the distance between the nuclei of 2 atoms covalently bonded together
when comparing covalent bonds formed between 2 atoms of the same element, what is the relationship between bond length and bond strength
the shorter the bond the greater the bond strength
because there is an increased electrostatic attraction between the 2 nuclei and the electrons in the overlapping atomic orbitals