Honors Chemistry: Unit 2 Review

how many electrons are involved when two atoms in a molecule are connected by a double bond? triple bond?

4 electrons; 6 electrons

octet rule

8 electrons are required to fill in the s and the p orbitals in the valence energy level. exception: duet rule (2 electrons) for hydrogen.

chemical properties

ability of a substance to undergo a specific chemical change

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

allow free electrons to move between the atoms (not associated with single atom or covalent bond)

matter

anything that takes up space and has mass

bonding pairs vs lone pairs vs terminal atom

bonding pairs - e- that are shared between 2 atoms lone pairs - e- that are not involved in bonding terminal atom - an atom that has only one bonding site (thus found on end of molecule)

chemical change

change that produces matter with a different composition than the original matter

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 bond (type of bonding where electrons are shared by two nuclei); usually occur between nonmetals; will typically occur where an atom has a 1/2 filled orbital

which bond has lowest melting and boiling points?

covalent bonds (non-polar have very low, polar in between ionic and non-polar covalent)

properties of ionic compounds

crystalline solids at room temperature, generally have high melting points, can conduct an electric current when melted or dissolved in water

structural isomers

differ in the covalent arrangements of their atoms

law of conservation of mass

in any physical change or chemical reaction, mass is conserved. mass is neither created nor destroyed.

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 bond (an atom (metal) transfers electron(s) to another atom (nonmetal), which creates an electrostatic attraction of a positively charged ion and a negatively charged ion); these form between nonmetals and metals

which bond has highest melting and boiling points?

ionic bonds

which bond has greatest solubility? which has the lowest solubility?

ionic bonds; covalent bonds

formula unit

lowest whole # ratio of ions in an ionic compound

pure substance

matter that has a uniform and definite composition

which bond has highest conductivity? which has the lowest conductivity?

metallic bonds; covalent bonds

heterogenous mixture

mixture in which the composition is not uniform throughout

homogeneous mixture/solution

mixture in which the composition is uniform throughout

alloy

mixtures of two or more elements, at least one of which is a metal

molecule

neutral group of atoms joined together by covalent bonds

nonpolar vs polar covalent bond

nonpolar - covalent bond with equal sharing of electrons between the two nuclei polar covalent bond - covalent bond with unequal sharing of electrons between the two nuclei

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

nucleus and electrons in inner shell remain unaffected when atoms come close together; electrons in outermost shell of an atom get affected, so they are the ones shared and are responsible for formation of the bond,

electron promotion

one e- from a full s orbital moves to an empty p orbital in the same quantum level

structural formula

overall shape of the molecule is represented by elements, symbols, and a single covalent bond is represented by a straight line or dash

mixture

physical blend of two or more components

electrolysis

process in which electrical energy is used to bring about a chemical change, electrolysis of water produces hydrogen and oxygen

filtration

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

In 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.

put mixture in hot water + allow benzoic acid to separate, then funnel it and see what's on the funnel paper. heat the leftover water and see what's left after it evaporates.

physical properties

quality or condition of a substance that can be observed or measured without changing the substance's composition

element

simplest form of matter that has a unique set of properties

bonds

single bond - one pair of e- are shared between 2 atoms double bond - two pairs of e- are shared between 2 atoms triple bond - three pairs of e- are shared between 2 atoms

atom

smallest particle of an element that retains its identity in a chemical reaction

physical change

some properties of material change, but the composition of the material does not change

reactant

substance present at the start of the reaction

product

substance provided in the reaction

compound

substance that contains two or more elements chemically combined in a fixed proportion

properties of metals

(due to the metallic bonding) good conductors of electric current and heat, malleable, ductile

Lewis structure

- A structural formula in which electrons are represented by dots; dot pairs or dashes between two atomic symbols represent pairs in covalent bonds. - representation of a molecule that shows how the valence e- are arranged among the atoms in the molecule

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 contains polar bonds mean that the whole molecule will also be polar?

- a polar covalent bond is a covalent bond in which the atoms have an unequal attraction for electrons, and so the sharing is unequal (in a nonpolar bond, the atoms have equal attraction for electrons, so the sharing is equal) - large differences between electronegativity of the bonded atoms increase polarity; polarity depends on electronegativity of bonded atoms; - not all molecules having polar bonds are polar - generally if difference is less than 0.4, bond is considered nonpolar but if difference is greater than 0.4, bond is considered polar - polarity of a bond depends on the difference between the EN values of the atoms forming the bond

describe how the process of distillation could be used to separate into its component substances.

- based on vaporization of the different components of the mixture to be separated - mixture is heated, vapors are produced, separated, then condescend back into liquid

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 share electrons to fill valence orbitals - ionic compounds have metals transfering e- to nonmetals, so each will have a full valence orbital

describe how the process of filtration could be used to separated a mixture into its components.

- using funnel lined with filter paper to retain solids while letting liquid through

lewis structure for polyatomic ions

-add one electron for each negative charge -subtract one electron for each positive charge

how to find dipole moment? which end is a partial positive and which is a partial negative?

-atom with the higher EN is partially negative, δ -

VSEPR chart

1) no. of electron pairs = 2, bonds = 2, electron pair arrangement = linear (180 degrees), partial lewis structure = A-B-A, molecular structure = linear 2) no. of electron pairs = 3, bonds = 3, electron pair arrangement = trigonal planar (triangular, 120 degrees), partial lewis structure = A-B-A | A , molecular structure = trigonal planar (triangular) 3) no. of electron pairs = 4, bonds = 4, electron pair arrangement = tetrahedral (109.5 degrees), partial lewis structure = A | A - B - A | A , molecular structure = tetrahedral 4) number of electron pairs = 4, bonds = 3, electron pair arrangement = 4, partial lewis structure = - - A - B - A | A, trigonal pyramid 5) number of electron pairs = 4, bonds = 2, electron pair arrangement = tetrahedral, partial lewis structure = - - A - B - A - - , molecular structure = bent or v-shaped

lewis structure guidelines

1. determine total # of valence e- (add them up for all atoms in the molecule) (for polyatomic anion, add e- for each negative charge for polyatomic cation subtract e- for each positive charge) 2. put the least EN atom in the center or the atom needing the most bonds (hydrogen always goes on the outside) 3. put 2 e- between atoms to form chemical bonds 4. complete octets on outside atoms (or duets for hydrogens); then finish putting any remaining valence e- around central atom (lone pairs) 5. if central atom(s) does not have an octet, move e- from outer atoms to form double and/or triple bonds

although both the BF3 and NF3 molecules contain the same number of atoms, the BF3 molecule is trigonal planar while the NF3 molecule is trigonal pyramidal. explain.

BF3 has 3 e- areas (3 bonded and zero lone pairs) so the molecule is flat (2-D) - trigonal planar. NF3 has 4 areas of e- (3 bonded and 1 lone pair) - the lone pair of e- gives the molecule a tetrahedral electronic shape and makes the molecular shape be 3-D (the lone pair created the point of the pyramid).

lewis structure calculation

N - A = S # electrons needed (octet or duet) - # electrons available (valence electrons) = # electrons shared (bonding electrons)

What is the VSEPR theory?

Valence Shell Electron Pair Repulsion theory; states that the repulsion between valence electron pairs/regions causes molecular shapes to adjust so that the valence-electron pairs/regions stay as far apart as possible

what is the geometric structure of the water molecule? how many pairs of valence electrons are there on the oxygen atom in the water molecule? what is the approximate H-O-H bond angle in water?

Tetrahedral; bent; 2 lone pairs and 2 bonded pairs of e-; 109 degrees

molecular compound

a compound composed of nonmetals covalently bonded together as individual molecules; properties: tend to have relatively lower melting and boiling points than ionic compounds, many are gases and liquids at room temp

what is a chemical bond?

a force that holds groups of 2 or more atoms together to function as a unit (molecule)

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

tendency of an atom participating in a covalent bond to attract the bonding electrons in a molecule; it is the measure of an atom's ability to attract shared electrons to itself; increases left to right across a period and decreases as you move down a group; higher the atom's electronegativity, closer the shared electrons tend to be to that atom when it forms a bond

what is the geometric structure of the methane molecule, CH4? how many pairs of valence electrons are present on the carbon atom of CH4? what are the approximate H-C-H bond angles in CH4?

tetrahedral, with 4 equal bond angles of 109.5 degrees and 4 equal bond lengths; 8 valence electrons, 4 available pairs; all angles are 109.5 degrees

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

tetrahedral; trigonal pyramid; 1 lone pair and 2 bonded pairs of 3-; 109 degrees

metallic bond

the forces of attraction between the free-floating valence electrons and the positively charged metal ions

molecular structure

the shape of the molecule focusing on the atoms bonded to the center atom

electronic structure

the shape of the molecule focusing on the lone electrons and the bonded atoms around the center atom

how is VSEPR used to predict the arrangement of electron pairs about the central atom?

to predict the molecular geometry of a molecule, a double bond or triple bond is counted as one region of electrons; molecule is polar (has an overall dipole moment or dipolar) when the dipole moments of the bonds do not cancel out

boron trifluoride is an exception to the octet rule. what is the geometric structure of the boron trifluoride 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?

trigonal planar; trigonal planar; 0 lone pairs and 3 bonded pairs of e-; 120 degrees

distillation

when a liquid is boiled to produce a vapor that is then condensed into a liquid