Flashcards in Ionic And Covalent Bonding Deck (37):
What is a compound give an example
It is when two or more elements combine in a chemical reaction eg, hydrogen gas is burned in oxygen gass, water is formed
Give one difference between elements and compounds?
Elements cannot be broken down into simpler substances whereas compounds can eg, if electricity is passed through water it breaks down into hydrogen and oxygen
What does a chemical formula tell you?
What elements are present and in what relative proportions
What is water of crystallisation?
It's water chemically combined in definite proportions in a crystalline compound
Give an example of noble gas uses
Helium - wearer balloons and blimps
Argon - in light bulbs
What is the octet rule?
Atoms on reaction tend to reach an electron arrangement with eight electrons in the outermost energy level
What are exceptions to the octet rule?
Beryllium and boron have few electrons in the outer levels so they cannot gain enough electrons to reach eight in the outer level
The d block elements don't usually obey the octet rule
Hydrogen and lithium atoms tend to reach electronic structure of helium but unable to gain large number of electrons
What is the valency?
It's the number of reactions an atom of the element forms when it reacts
What does valency measure?
The combining power of an atom
Where will you normally find ionic bonds?
Compounds that contain metals with non-metals.
What is an ionic bond?
It's the electrostatic force of attraction between oppositely charged ions
What does ionic bonding result in?
Not a compound, but a lattice
What is a lattice
Each ion in a lattice is surrounded by others of opposite charge
How is the structure of crystal lattices determined?
By X-ray technique
Characteristics of ionic substances
High melting points - the strong forces of attraction means there is a lot of energy needed to break up the lattice - solids at room temp
Conduct electricity when in molten state - ions have been freed
Most dissolve in water, water is polar are attracted to ions
What's the test for carbonate and hydrogen carbonate?
Both react : dilute hydrochloric acid
Reagent : magnesium sulfate
On heating : hydrogen carbonate turns into carbonate
White ppt : carbonate
What is the test for sulfate and sulfite?
Both react : barium chloride
Reagent : hydrochloric acid [barium sulfite]
White ppt : sulfite
What is the test for chloride?
Silver nitrate = white ppt = dissolved in ammonia
What is the test for nitrate?
Iron II sulfate + conc sulfuric acid = brown ring
Test for phosphate
On heating w/ ammonium molybdate = yellow ppt = dissolved by ammonia
Test for anions procedure
1. Add 2cm3 of solution to a test tube and then add they both react with
2. White ppt indicates presence of sulfate/sulfite ions/ c02 is produced = limewater
3. Add reagent and what is white ppt
4. Repeat and for hco3 remember to mention heating
What is a covalent bond?
It is formed when two atoms share a pair of electrons
What are lone pairs?
Pairs of electrons not involved in the bonding
How are the strengths of covalent bonds measured?
Measuring energy needed to break the bond
What occurs in a single covalent bond
Atomic orbitals overlap end on to eachother [ two s orbitals, two p orbitals or an s and a p orbital]
What occurs in a double bond?
Sideways overlap between two p atomic orbitals each containing one electron = pi bond
What occurs in a triple covalent bond?
2 pi bonds and 1 sigma bond overlapping sideways
What is a non polar molecule?
Its a pure covalent bond where electrons are equally shared
What factors dictate where the shared electrons are attracted to
The size of the atom - stronger attraction than larger atoms so shared electrons can get closer
Nuclear charge - atoms with bigger charge in nucleus will have a greater charge
What are polar covalent bonds?
When electrons are shared unequally
In a polar covalent bond, what becomes positively/negatively charged?
The atom with lesser share of electrons = slightly positively charged
Atom with more = slightly negatively charged
What are the characteristics of covalent substances?
Low melting and boiling points - gases at room temp
Do not conduct electricity - neutral molecules
Do not dissolve readily in water
Give examples of polar materials in every day life
Polar - water [washing clothes] + glucose [lucozade]
Non polar - Petrol
What is electronegativity?
It's the relative attraction of an atom for shared pairs of electrons in a covalent bond
The higher the electronegativity value, what effect does it have?
It better it is at attracting the shared electrons
Where does the electronegativity increase on the periodic table and why?
-atomic number increases, nuclear charge
-no screening since extra electrons are added to the same outer shell therefore atomic radius decreases
-both these = the greater the attraction