Fall Semester Review Questions

Atoms, Periodic Table, and Molar Mass Problems

2010

What type of elements give off valence electrons to achieve a configuration of a noble gas?

• Metals give off valence electrons.

Metals form cations

How is a covalent bond formed?

• Covalent bonds are formed when electrons are shared to complete an octet.

Write the Lewis structure for NH3

• Are the bonds between N and H covalent or ionic?

• How many bonds does N form?

• How many bonds does H form?

Covalent bonds, 3 with N and 1 with H. Completing octet for N and duo for H.

What type of elements receive valence electrons to achieve a configuration of a noble gas?

• Non-metals that form anions• Elements with high electronegativity

How is an ionic bond formed?

• Ionic bonds are formed when electrons are transferred from a cation to an anion.

• Electrostatic interactions

Write the Lewis structure for CO2

Which group of metals is the most chemically active?

• Alkali Metals – activity increases down the group

Write the Lewis structure for F2

How many bonds in this NON-POLAR Covalent Diatomic Molecule?

A single bond = 2 shared electrons

Write the Lewis structure for C2H4

What kind of bondsDoes C have?

COVALENT BondsTwo bonds in C because four Electrons are SHARED

Which group of nonmetals is the most chemically active?

Halogens – Group 7A or 17

The most active element of the group is Fluorine!

Write the Lewis structure for O2

The composition of a compound contains only C, O, and H atoms.

What type of bond does the compound have?

• All NON-Metals so bonds must be COVALENT

According to the periodic table, which two elements in each set of elements

will likely form an ionic bond? A 1 14 17 18B 2 3 17 18

• A-B• 1-17 An alkali metal with a halogen• A 1+ with a 1-

A compound consists of two elements whose electronegativities are 2.20 (H)

and 3.16 (Cl). What is the percent ionic character of the bond they form?

Step 1 figure out the difference

3.16-2.20 =0.96 electronegativity difference

Step 2 estimate how polar the covalent bond is: <1 difference is less than 25% ionic so the bond would be considered polar covalent

Given the chemical formula of a compound, how will you tell whether the compound is

an ionic compound or molecular compound?

• Check the elements:

– If a metal and non-metal

= ionic bonds

– If non-metal and non-metal

= covalent bonds

Ionic Compound – ionic bond (formula unit)

Molecular Compound – covalent bond

Elements in the same group have similar physical and chemical

properties because they have the same number of _____________?

• Valence electrons = outermost electrons

Of the seven diatomic molecules, which one contains a double bond?

A triple bond?

• The seven diatomic molecules are:

–H2, O2, N2, F2, Br2, I2, Cl2

• Notice all are off by one except for O2 (off by 2) and N2 (off by 3).

• O2 is double bonded and N2 is triple bonded

Write the Lewis structure for N2

What type of elements have atoms arranged in crystal lattice structure?

Solid, liquid or gas?

Which groups on the periodic table would form ions with the following charges: a. 1+ c. 2+ b. 1- d. 2-

• a. 1+ = Alkali metal (Group 1A) • b. 1- = Halogen non-metal (Group 7A)• c. 2+ = Alkaline Earth Metal (Group 2A) • d. 2- = Chalcogens (Group 6A)

Show how you determine the mass of one mole of CO2

• Mass of one mole = Molar Mass• Count elements and atoms

C-1 @ 12 grams/mole = 12.

O-2 @ 16 grams/mole = 32 44

g/mole

In the periodic table, what group of elements has the most stable valence

electron configuration in the ground state?

Using the electronegativity values, how would you

know if the bond between two atoms is ionic? • Determine the electronegativity of each element.• Find the difference between electronegativities • Bond type can be described as belonging to one of

three classes: – nonpolar covalent– polar covalent– ionic

• When differences are 1.7 or greater = usually ionic.• Less than 1.7 to 0.5 = usually polar covalent, • Differences of less than 0.5 are considered to be

nonpolar covalent.

Show how you determine the mass of one mole of Mg(C2H3O2)2

• Mass of one mole = Molar Mass• Count elements and atoms

–Mg-1 @ 24.3 grams/mole= 24.3–C - 4 @ 12 grams/mole = 48.04–H - 6 @ 1 grams/mole = 6.06–O - 4 @ 16 grams/mole = 64.00

142.4 g/mole

In a binary ionic compound, one of the elements is Cl. Which of the following

would the other element most likely to be?Cl I Mg Br

• Binary = two parts• Since Cl-Cl would be covalent – not

right and the same would be for the other halogens:I, and Br.

• Mg is a metal forms a cation with +2 ox

• Ionic compound with cris-cross: MgCl2

Given different pairs of atoms, how would you decide which has the most

polar bond?

• I would first deal with covalent vs ionic –Non-metals with non-metals = covalent–Metals with non-metals = ionic

• If I was dealing with a covalent to estimate polarity I would look at differences in electronegativity estimated by position of the periodic table. Close not so, Far more so except for H.

Show how you determine the mass of one mole of Fe(NO3)3

• Mass of one mole = Molar Mass• Count elements and atoms

– Fe-1 @ 55.8 grams/mole = 55.8 g·mol−1 – N - 3 @ 14 grams/mole = 42.0– O - 9 @ 16 grams/mole = 144.00

241.8 g/mole

What’s the oxidation state of the Iron?????

What are the seven diatomic molecules?

• The seven diatomic molecules are:

–H2, O2, N2, F2, Br2, I2, Cl2

The Lewis structure of an atom has eight dots. Name the elements with

the same Lewis structure.

Noble Gases all have eight valence electrons except for Helium which is happy with 2 (1s2)

Given several bars of different metals each containing one mole. Identify the metals with the following approximate masses.

27 g c. 59 g65 g d. 40 g

• Periodic Table – my friend

27 g = Al 65 g = Zn

59 g = Co 40 g = Ca

Which part of the periodic table are these located?

metals __________nonmetals _________metalloids _________

• metals on the Left and Middle• nonmetals on the Right• metalloids on the BOLD line except Al

Which one has a larger ion than its neutral atom?

a. Ca b. Fc. Zn d. Cs

• Calcium loses electrons – gets smaller• Fluorine gains electrons – gets bigger• Zinc loses electrons – gets smaller• Cs loses electrons – gets smaller

What type(s) of elements would make a. ionic bond

b. covalent bond

• ionic bond: Metal and Non-metal or a Polyatomic cation and a non-metal or a polyatomic cation and polyatomic anion or a metal and a polyatomic anion

• covalent bond – between non-metals• metallic bond – between metals

What are some characteristics of ionic compounds

• Hard• High melting point• Conducts electricity when melted or

dissolved in water

What are some characteristics of Covalent Compounds

• Soft• Low melting point• Does not conduct electricity