Module 2 - bonding, structure, reactions etc Flashcards
What is made when you neutralise an acid with a metal oxide or hydroxide?
A salt + water
E.g. copper oxide + sulfuric acid
-> copper sulfate + water
What is made when you react an acid with an alkali?
A salt + water
E.g. HCl + NaOH -> NaCl + H2O
What are acids and bases defined as ?
Acids are proton (H+) donors.
Bases are proton acceptors
Define an alkali
A base that dissolves in water releasing hydroxide ions into the solution (OH-)
What defines the strength of an acid?
The strength of an acid is determined by how much it dissociates in water
A strong acid will ionise more in water, leaving more H+ ions available to react with other compounds
A weak acid will not ionise as much in water, so there are less protons available to be donated
What is made when you react an acid with a metal carbonate?
A salt + water + carbon dioxide
E.g. Magnesium carbonate + hydrochloric acid -> magnesium chloride + water + carbon dioxide
What are the special cases for oxidation numbers of certain elements in compounds?
H in metal hydrides is -1 (e.g. NaH, CaH2)
O in peroxide’s is -1 (e.g. H2O2)
O bonded to F is +2
While there are many different forms of sulfur and nitrogen, what is the common oxidation number assumed to these 2 elements in a compound ?
Unless you can work it out to be otherwise (eg. You know the oxidation number of everything except sulfur in a compound),
Nitrogen is assumed to be +5
Sulfur is assumed to be +6
So if you have sulfur/nitrogen plus another element with an unknown oxidation number, assume the numbers above for those two.
What change in oxidation number constitutes a reduction or oxidation reaction?
Reduction is a decrease in oxidation number
Oxidation is an increase in oxidation number
What is made in a reaction between a metal and an acid
A salt + hydrogen
What is an orbital
An orbital is the space in which an electron moves
What shape is an S-orbital
Spherical
What shape is a P-Orbital
Dumbbell shaped
When doing the electron configuration, why must electrons must be represented by 2 arrows in different directions?
To represent the two electrons in each orbital spinning in opposite directions
When writing electron configurations of ions, how are they different?
You need to remove or add electrons to or from the highest-energy occupied subshell
What is ionic bonding?
An ionic bond is an electrostatic attraction between two or more oppositely charged ions
What is a ‘giant’ structure
A compound which is made up of the same basic unit repeated over and over
What behaviours of ionic compounds are explained by its ionic structure?
- high melting point and boiling point, strong ionic bonds
- conduct electricity when molten or dissolved. The ions in a liquid are mobile and carry a charge, but are fixed when it’s solid
- can dissolve in water. Water molecules are polar so can attract charged ions
What is a covalent bond?
A covalent bond is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Name 2 examples of special covalent compounds
- In boron trifluoride, boron has only 6 electrons in its outer shell
- In sulfur hexafluoride, sulfur has 12 electrons in its outer shell
What is dative covalent bonding
Where both electrons come from one atom in a covalent bond
E.g. NH4+ is formed by dative covalent bonding. The nitrogen atom donates a pair of electrons to H+
How is dative covalent bonding sometimes represented (when drawing the displayed formula of one)
An arrow is drawn from the ‘donor’ atom to the non donor
What determines the shape of a molecule
- number of atoms involved in the molecule
- number of lone pairs of electrons
What is ‘electron pair repulsion theory’
Electrons are all negatively charged, so electron pairs will repel each other as much as they can
The number of electron pairs in bonds and lone electron pairs determines the structure of a molecule
How would you draw a molecule with 2 electron pairs around a central atom?
What is the bond angle?
It’s a straight line, ‘linear’
Bond angle of 180 degrees
What shape does 3 electron pairs around a central atom make?
Bond angle?
Central atom with 3 bond pairs equally placed in a triangle shape
Bond angle = 120 degrees
What shape does 4 electron pairs around a central atom make (NO LONE PAIRS)?
Bond angle?
Tetrahedral shape. Triangular based pyramid with another bond pair going above the top, central atom. See pg 47 revision guide
Bond angle 109.5 degrees
What shape does a central atom with 4 electron pairs around it make (ONE LONE PAIR)?
Bond angle?
Trigonal pyramidal. Triangular based pyramid with 2 electrons on top of the top atom
Bond angle 107 degrees
What shape does 4 electrons around a central atom make? (2 LONE PAIRS)
Bond angle?
Makes a v-shape, “bent”, or “nonlinear” with 2 lone pairs on one side and 2 bond pairs on the other side making a V
Bond angle = 104.5
What shape does a molecule with 5 electron pairs around a central atom make? Bond angles?
Makes a “trigonal bipyramidal” shape. It’s like 2 triangular based pyramids with their bases attached together.
Some of the bond angles are 90 degrees and some are 120 degrees
What shape does a molecule with 6 electron pairs around a central atom make? Bond angle?
Octahedral shape. 2 square based pyramids with their bases joined together
Bond angles of 90 degrees (all)
Define electronegativity
An atoms ability to attract the electron pair in a covalent bond
What is the general trend for electronegativity?
As you get further right and further up the periodic table, they get more electronegative.
Fluorine is the most electronegative (top right)
What are the general properties of substances that have hydrogen bonding?
Soluble in water
Higher boiling and freezing points
What elements can form hydrogen bonds when in hydride form?
Nitrogen, fluorine and oxygen
Why do simple covalent compounds have low melting and boiling points?
The intermolecular forced between the molecules are weak so don’t need much energy to break
What is the oxidation rule for elements on their own?
The oxidation number is always 0 for elements on their own
What is the oxidation number of a compound made of the same element?
Compounds with multiple of the same element e.g. H2, O2, P4 etc are always 0
What is the rule for the oxidation numbers of the elements in an ionic compound?
The oxidation number of an ionic compound will always add up to the charge on that compound
What rule relates oxidation number and the charge of the compound it is found in?
The sum of the oxidation numbers is equal to the charge of the compound
What is the oxidation number of an element?
Generally, the oxidation number of an element in a compound is the same as the charge for that element to become a stable ion
