practice test for science unit 3 test

This is an atom that has lost or gained electrons. Example: sodium with a positive charge, oxide with a two negative charge

Ion

the number below and to the right of an element in a chemical formula. It represents the number of atoms of that element in chemical compound or molecule. Example: The 2 in H2O

subscript

The electrostatic attractions in crystalline salts, such as sodium chloride, are formed by __________ between positive and negative ions.

transferring electrons

the electrostatic attractions in crystalline salts, such as sodium chloride, are formed by __________ between positive and negative ions.

transferring electrons

Ionic and covalent bonds

Atoms vibrate about fixed mean positions within the ordered solid.

Solution What it is made of A Water and Salt B Water and Sugar C Water and HCl D Water and NaOH Which of these substances would be a poor conductor of electricity?

B Water and sugar would be a very poor conductor of electricity. The other choices all contain ionic compounds. When they form a solution, the charged ions allow for the flow of electricity. Sugar is a covalent compound. When in solution, it does not form ions, thus it will not allow for electricity to flow

covalent bonds

bad electrical conductors in all phases The atoms are bound tightly to each other in stable molecules, but those molecules are generally not very strongly attracted to other molecules in the material. The forces between molecules are weak, so most have low melting and boiling points.

A compound composed of two oppositely charged elements. Example: NaCl, MgO, Li2O

binary ionic compound

H2O Cl2 NH3 What do all of these compounds have in common?

They are all covalent.

Nitrogen can ionically bond with an unknown element X from group 2. How many ions of element X are required to create a stable ionic compound with nitrogen?

3

Which statement describes how a covalent molecule would be formed? A) an atom of an element with atomic number 12 reacts with one oxygen atom B) an atom of an element with atomic number 8 reacts with two hydrogen atoms C) an atom of an element with atomic number 20 reacts with two fluorine atoms D) two atoms of an element with atomic number 11 react with one sulfur atom

A covalent bond is formed by sharing electrons. An atom of an element with atomic number 8 has two valence electrons. A hydrogen atom has one valence electron. So an atom of an element with atomic number 8 reacts with two hydrogen atoms.

If you want to conduct an electrical current, which situation would produce a solution capable of this?

Dissolving solid NaF in water

How is electron movement related to the bonding in sodium chloride?

Electrons exchange creating ions to form an ionic bond by electrostatic attraction.

Which substance(s) will be good conductors of electricity? I. H2O (s) II. NaCl (s) III. NaCl (l) IV. Au (s)

III and IV only

In ____________, electrons are gained by atoms and lost by others.

Ionic bonds occur between metals and nonmetals. Metals have fewer valence electrons than nonmetals and will give their valence electrons to a nonmetal in order to become more stable.

Which of these BEST describes why an ionic solution is a good conductor of electricity while a covalent solution is a poor conductor?

Ionic compounds form charged molecules in solution, and electricity will only flow if charged molecules are present. Charged particles are called ions and ions assist in the flow of electrons. Ionic compounds produce these charged ions while covalent compounds do not

Because of the nature of ionic and covalent bonds, the materials produced by those bonds tend to have quite different macroscopic properties. Can you pick out the properties of ionic solids, like the solid illustrated above, sodium chloride?

Ionic compounds have enthalpies of fusion and vaporization that may be 10 to 100 times higher than most molecular compounds. When pressure is applied to an ionic crystal the ions of like charge are forced close together forcing the crystal to split. Ionic solids do not conduct electricity very well because the ions are bound so tightly to each other.

ionic bond

Many soluble in water but not in nonpolar liquid High lattice energies results in high melting points.

An atom of an element with two valence electrons reacts with two atoms of an element with atomic number 17 to form an ionic compound. What is the compound MOST LIKELY formed as described?

MgCl2

This is a compound made from a group of covalently bonded atoms. Example: carbon dioxide, methane, water

Molecule

Unknown element X is a metal that ionically bonds to sulfur. Is the formula, X3S feasible? Why or why not?

No, it is not feasible. Three metallic ions cannot provide the exact number of electrons that one sulfur needs for the ionic bond.

Sulfur hexafluoride is represented by which formula?

SF6

Sodium chloride comprises 97%-99% of table salt. Given their location on the periodic table, identify the ionic charge for each element and predict the chemical formula of the compound formed.

Sodium, Na, is an alkali metal and is in Group IA with an ionic charge of +1. While chlorine, Cl, is a halogen and is in Group VIIA with a charge of -1. These will form NaCl(s).

Ionic solutes are considered strong electrolytes. What does this mean for the conductivity of the solution?

Strong electrolytes dissolve and completely dissociate in water providing charged ions to conduct electricity.

What is the chemical formula for potassium oxide?

The correct formula for potassium oxide is K2O. First, be sure you have the correct symbols for each element. Then check the oxidation/valence number: potassium (K) is +1 and oxygen (O) is -2. Using the criss-cross method to be sure that the sum of the oxidation numbers equals zero, we have K2O.

K2O Use IUPAC nomenclature rules to properly identify this compound.

The correct name is potassium oxide. It is a binary ionic compound, so no prefixes are used. Since potassium is a representative metal with only one possible charge, no roman numerals are used.

Ionic compounds molecules have strong forces of attraction between neighboring molecules. Which conclusion could be drawn about materials held together by ionic bonds?

These materials would have very high boiling points. Ionic compounds have high boiling points and tend to be solids at room temperature.

Using IUPAC nomenclature, give the name of BH3 and AlH3 and elaborate why that name is correct

boron trihydride - boron and hydrogen are both non-metals and form covalent bonds. aluminum hydride - aluminum is a main group metal and hydrogen is a non-metal and they form ionic bonds.

Ionic bonds are based on the _________ of the elements.

charge

Shows the number and type of atoms present in the smallest representative unit of a substance. Example: NH3, H2O

chemical formula

This is two or more elements chemically combined in a fixed ratio. Example: water, carbon dioxide, sodium chloride

compound

The ability or power to transmit heat, electricity, or sound. Example: Metals transfer heat, electricity, and sound better than nonmetals.

conductivity or conductor

Water, H2O, is a molecule made of oxygen and hydrogen. The bonds that hold water molecules together are due to shared electrons, and known as __________ bonds.

covalent

Water, H2O, is a molecule made of oxygen and hydrogen. The bonds that hold water molecules together are due to shared electrons, and known as __________ bonds. In contrast, the bonds that hold NaCl molecules together are _________ bonds, arising from a charge difference between the atoms.

covalent; ionic

Water, H2O, is a molecule made of oxygen and hydrogen. The bonds that hold water molecules together are due to shared ___________, and known as covalent bonds

electrons

Water, H2O, is a molecule made of oxygen and hydrogen. The bonds that hold water molecules together are due to shared ___________, and known as covalent bonds.

electrons

Covalent bonds occur when ________________.

electrons are shared between atoms

Sodium chloride, NaCl, is formed when a sodium atom transfers its electron to a chlorine atom. The difference in charge between the two atoms creates a(n) ___________ attraction that bonds them together.

electrostatic

This is a substance that cannot be broken down further by chemical means. Example: sodium, tungsten, iodine

element

The electrostatic attraction that binds oppositely charged ions together. Example: Na+ + Cl- NaCl

ionic bond

Crystalline salts such as cesium bromide form _____ bonds with __________.

ionic, electrostatic attractions

This is a property of matter that can be identified without changing the identity of the substance. Example: weight, color, odor, boiling point, density

physical property

Metallic ions or cations are __________ charged ions.

positively

the illustration depicts the formation of an ionic chemical bond between sodium and chlorine atoms. The result of this bonding is a chemical compound that is stable because the

shared electron provides provides sodium with a full outer energy level.