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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


Where does the electronegativity decrease and why?

Down the group
-extra energy levels cause shielding of outer electrons from nucleus = increase in atomic radius
-although the nuclear charge is increasing, not attracted strongly
-greater screening, increased atomic radius reduces attraction for shared pairs of electrons