Gr.9 Science: Valence, Compounds & Trends Chemistry Unit

What does the group number represent

number of valence electrons

What does the period number represent

number of total shells

Difference between atoms and ions?

atoms are neutral and ions are charged

Why is the valence shell important?

it determines an atoms chemical properties and is first part to make contact with other atoms

What is an octet structure?

atom with full valence shell (8VE)

What is an duet structure?

atom with valence shell with 2 valence electrons (2VE)

Three ways to write ionic compounds

-Lewis Drawing

-Algebraically by inspection

-Crisscross charges method

What is Bohr Rutherford Drawing

normal Bohr Rutherford atom model with square brackets and charge

What are the two kinds of Compounds

ionic (both) and molecular (NMs only)

How to write Ionic compounds

criss-cross method and IDE ending

How to write molecular compounds

Greek prefixture (Mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca) and IDE ending

How are ions formed?

When atoms lose or gain electrons

What can ions achieve together?

Net charge of zero

e's ____ by metal must be _____ to e's ______ by non-metals

lost, equal, gained

Trend in ion formation charges?

1, 2, 3, -4, -3, -2, -1, stable

Why are compounds formed?

To achieve a full valence shell

List properties of ionic compounds

-Good conductor of heat & electricity

-High MP & BP

-Ionic bond

List properties of molecular compounds

-Poor conductor of heat & electricity

-Low MP & BP

-Covalent bond

What is the periodic law?

when the elements are in order of increasing atomic number, there is repetition of their properties

What is an effective nuclear (Zeff) charge?

attraction between the valence electrons and the nucleus protons.

effective nuclear (Zeff) is always ____ than protons in the nucleus because of shielding effect

less

What is the shielding effect?

Interference with the attraction between nucleus protons and valence electrons

What does shielding effect increase with?

Number of inner shells and electrons

The ______ shielding effect the lower Zeff

higher

Where does Zeff increase and why

To the upper right because there is no increasing shielding effect

Where does Zeff decrease and why

To the lower left because shielding effect counters the increasing nuclear charge

What is atomic radius?

size of an atom

Where does atomic radius increase and why

Lower left because adding of shells

what is chemical reactivity?

ability to undergo a chemical change to achieve full valence shell (to become more stable)

Trends in chemical reactivity in metals

- Increases toward the lower left

-Towards the bottom left is easier to lose electrons

Trends in chemical reactivity in non-metals

-Towards upper right reactivity increases

-Towards upper right is easier to gain electrons

What does lower Zeff make easier?

lose e's

What does higher Zeff make easier?

gain e's

What is an element?

a Substance that contains only ONE type of atom.

What is a compound?

2 or more elements chemically combined

What is a heterogeneous mixture?

a mixture in which the composition is not uniform throughout

What is a homogeneous mixture?

a mixture that is the same throughout