chemistry Unit 2 test

Why are the valence electrons of an atom the only electrons likely to be involved in bonding to other atoms?

e- in full energy levels (core e-) do not need to gain or lose e- to have full orbitals. Only valence orbitals need to gain or lose e- to achieve a noble gas configuration.

Mixture

is a physical blend of two or more components

pure substance

matter that has a uniform and definite composition; either an element or a compound

Matter

only substance that has mass and take up space by volume

electrolysis

process by which electric current is passed through a substance to effect a chemical change

Law of Conservation of Mass

states that in any physical change or chemical reaction, mass is conserved

What does it mean to say that a bond is polar? What are the conditions that give rise to a bond's being polar? Does the fact that a molecule possess polar bonds mean that the molecule itself will also be polar?

A bond is polar when the shared e- are closer to one of the bonded atoms (due to that atom having a larger electronegativity value). The greater the electronegativity difference, the more polar the bond. If the dipole moments of each bond cancel out (due to strength and shape of the molecule) then the molecule is nonpolar.

physicle change

A change in the substance that does not change its original properties may appear different

physical properties

A characteristic of a pure substance that can be observed without changing it into another substance

Reactant

A chemical substance that is present at the start of a chemical reaction

What is a chemical bond?

A force that holds groups of 2 or more atoms together.

distillation

A process that separates the substances in a solution based on their boiling points

product

A substance formed as a result of a chemical reaction

n a lab, students are asked to determine the relative amounts of benzoic acid and charcoal in a solid mixture. Benzoic acid is soluble in hot water, but charcoal is not. Devise a method for separating the two components of this mixture.

Add hot water to the sample. This will dissolve the benzoic acid but not the charcoal. The hot sample can be filtered through filter paper, which will remove the charcoal (it will stay in the filter paper) while the solution of benzoic acid will go through the filter paper. Allow the solution to cool so that the benzoic acid will crystallize back out. Then the benzoic acid can be filtered out. Allow both components to dry and then find their masses.

How can we show the dipole moment of a polar bond?

An arrow drawn next to the bond with the arrow head pointing toward the partial negative end or a low case delta symbol with a + or -.

intensive property

a property that depends on the type of matter in a sample, not the amount of matter

Although both the BF3 and NF3 molecules contain the same number of atoms, the BF3 molecule is flat whereas the NF3 molecule is trigonal pyramidal. Explain.

BF3 has 3 e- areas (3 bonded & zero lone pairs) so the molecule is flat (2-D) - trigonal planar. NF3 has 4 areas of e- (3 bonded & 1 lone pair) - the lone pair of e- givens the molecule a tetrahedral electronic

atom

Basic unit of matter Smallest particle of an element

What type of bonding involves the sharing (either equally or unequally) of electrons between atoms? What type of atoms usually make this type of bond?

Covalent - nonmetals only

Explain how the atoms in covalent molecules achieve configurations similar to those of the noble gases. How does this differ from the situation in ionic compounds?

Covalent molecules: atoms (nonmetals) share e- to fill valence orbitals (s & p) Ionic compounds: metals transfer e- to nonmetals, so each will have full valence orbitals

Describe how the process of distillation could be used to separate a solution into its component substances. Give an example.

Distillation can be used when the components of a mixture have different boiling points. Salt water; by boiling a solution of salt water, the water would boil off first leaving the salt behind. (Water has a lower boiling point than table salt.)

What do chemists mean by the term electronegativity? What does its electronegativity tell us about the atom?

Electronegativity is the relative ability of an atom in a molecule to attract shared e- to itself. The larger the electronegativity value, the closer the shared e- tend to be to that atom when it forms a bond.

What is the geometric structure of the ammonia molecule? How many pairs of electrons surround the nitrogen atom in NH3? What is the approximate H-N-H bond angle in ammonia?

Electronic structure = tetrahedral, molecular structure = trigonal pyramid, 1 lone pair

Boron trifluoride is an exception to the octet rule. What is the geometric structure of the boron triflouride molecule, BF3? How many pairs of valence electrons are present on the boron atom in BF3? What are the approximate F-B-F bond angles in BF3?

Electronic structure = trigonal planar, molecular structure = trigonal planar, 0 lone pairs & 3 bonded pairs of e-

elemet

a substance that cannot be separated or broken down into simpler substances by chemical means

Describe how the process of filtration could be used to separate a mixture into its components. Give an example.

Filtration can be used when the components of a mixture have different solubilities in water. A mixture of sand and salt; when adding water to the mixture, the salt will dissolve and the sand will not. When you pour the mixture through filter paper, the sand will stay in the filter paper while the salt water will go on through.

alloy

a substance that contains a mixture of elements and has metallic properties

What type of bonding requires the complete transfer of an electron from one atom to another? What type of atoms usually make this type of bond?

Ionic - metals w/ nonmetals

hetrerogeneous mixture

a mixture which compostion in sont uniform

extensive property

a property that depends on the amount of matter in a sample

Explain (on the particulate level) how metals conduct electricity.

The delocalized electrons (sea of free e-) are free to move around the positively charged metal ions.

Explain how the valence shell electron pair repulsion theory (VSEPR) is used to predict the arrangement of the electron pairs about the central atom.

The structure around a given atom is determined by minimizing repulsion between e- pairs.

Molecule

a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

homogenous mixture (solution)

a mixture in which the composition is uniform throughout

chemical properties change

the ability of substances to undergo a specific chemical property

Filtration

the process that separates a solid from the liquid in a heterogeneous mixture