CHEM 125 Exam 1

What is a pure substance?

a substance that has a definite composition

What are the two types of pure substances?

elements and compounds

What are the two types of mixtures?

homogeneous and heterogeneous

What is a mixture?

material composed of two or more elements or compounds that are physically mixed together but not chemically combined

What is an element?

simplest form of matter made of only on type of atom

What are compounds?

substances in which atoms of two

or more elements are chemically combined

What occurs in a chemical rxn?

The identity of the substances are altered

What occurs when you combine pure substances?

each retains their original properties

What is a homogenous mixture?

a mixture in which the composition is uniform throughout

What is a heterogeneous mixture?

a mixture in which the composition is not uniform throughout

What are the four techniques to physically separate a mixture?

filtration, distillation, chromatography, centrifugation

What are physical properties?

characteristics of a substance that can be observed without changing it into another substance

What are chemical properties?

properties that can only be observed when one substance changes into a different substance

What are examples of physical properties? (7)

viscosity, conductivity, malleability, hardness, melting point, boiling point, and density

What are examples of chemical properties? (4)

ability to burn, ability to rot, ability to react with water, ability to react with oxygen, etc...

What are the physical properties of water? (4)

- liquid at room temperature

- colorless

- freezing point is 0 degrees Celsius and boiling point is 100 degrees Celsius

What are the chemical properties of water? (3)

decomposed using electricity, reacts with K and Na, reacts with CO at high temps to make CO2 and H

What is energy?

the ability to do work

What are the two main types of energy?

kinetic and potential

What is kinetic energy?

energy of motion

What is potential energy?

stored energy

What do most chemical reactions involve?

the release or absorption of energy

What is the law of conservation of energy?

Energy cannot be created or destroyed

What is a measurement?

a quantity that has both a number and a unit

What is accuracy?

how close a measurement is to the true value

What is precision?

a measure of how close a series of measurements are to one another

How do you determine the "true" value?

you need the real value

How is precision expressed?

as standard deviation

What do significant figures indicate?

precision

What is an exact number?

those numbers obtained by counting items or using a definition that compares two units in the same measuring system ~ EQUALITIES

What is a measured number?

number that is obtained using equipment

The more the sig figs, the _ the precision.

higher

What are the significant figure rules?

1) non-zero digits are always significant

any zeroes between two significant figures are significant

2) zeroes in front of a number are never significant

3) zeroes at the end of a number and to the right of a decimal are significant

4) sometimes zeroes on the left of a decimal are significant

What is the rule for significant figures when multiplying and dividing?

answer must have the same number of sig figs as the term with the least sig figs

What is the rule for significant figures when adding and subtracting?

answer must have the same number of decimal places as the term with the least number of decimal places

What is the F temperature conversion equation?

1.8 (C) + 32

What is the K temperature conversion equation?

C + 273

What is the equation for density?

D=m/v

What is the equation for specific gravity?

density of substance/density of water

What does density depend on?

temperature

What are the units for specific gravity?

no units

What are the units for density?

g/cm3 or g/mL

What is the density of water?

1 g/mL

How is the periodic table arranged?

by increasing atomic number

Periods

Horizontal rows on the periodic table

Groups

Vertical columns on the periodic table

What is the relationship among periods on the periodic table?

elements have the same valence electrons in the same energy level

What are valence electrons?

electrons in the outermost shell

What do valence electrons determine?

reactivity of an atom

What is the 1A group?

alkali metals

What is the 2A group?

alkaline earth metals

What is the 7A group?

halogens

What is the 8A group?

noble gases

What are the A groups of the periodic table?

main group elements

What are the B groups of the periodic table?

transition metals

What are the characteristics of metals? (8)

solid at room temperature, luster, conductive, ductile, malleable, high melting points, form ions by losing e-, do not readily combine with one another

What are the characteristics of nonmetals? (8)

exist in all states of matter, low luster, poor conductivity, not malleable, not ductile, low melting points, form ions by gaining e-, combine with all elements well

What are the characteristics of transition metals? (4)

mixed properties, metallic luster, electrical conduction that increases with temp, semiconductors

What are allotropes?

Different forms of the same element

What are the elements that exist as polyatomic? (10)

Br2, I2, N2, Cl2, H2, O2, F2, O3, P4, S8

What are atoms composed of?

subatomic particles: protons, electrons, neutrons

What is a proton?

(+) charge, mass 1 amu

What is a neutron?

neutral charge, mass 1 amu

What is an electron?

(-) charge, mass less than 1, negligible mass

Where is the majority of an atoms mass?

nucleus

What is the nucleus of an atom comprised of?

protons + neutrons

What accounts for the majority of an atom's volume?

electrons

What is the relationship between e and p of neutral atoms?

they are equal

What is the atomic number?

the number of protons in an atom

What is the mass number?

Number of protons and neutrons

How is an isotopic designation written? (3)

mass number (upper left), atomic number (bottom left), and charge (upper right)

What is an amu?

1/12 the mass of a carbon-12 atom, 1.66x10^-24 g

What is an isotope? (5)

Atoms of the same element that have different numbers of neutrons, different mass number, but same atomic number, identical chem properties, different physical

What is true when an atom forms an ion?

the ion has the same number of electrons as the nearest noble gas

What type of ions do metals typically make?

cations

What type of ions do nonmetals typically make?

anions

What type of ion does H make?

loses e- to be H+

What is the size relation of cations?

They are smaller than parent molecule

What is the size relation of anions?

They are larger than parent molecule

What ions do transition metals typically form?

cations

What are the three transition metal exception molecules?

Ag+, Zn2+, Cd2+

Ammonium

NH4+

hydroxide

OH-

Cyanide

CN-

Chromate

CrO4 2-

Dichromate

Cr2O7 2-

Permanganate

MnO4-

Phosphate

PO4 3-

Hydrogen Phosphate

HPO4 2-

Sulfite

SO3 2-

Sulfate

SO4 2-

Nitrite

NO2-

Nitrate

NO3-

Hydrogen carbonate (bicarbonate)

HCO3-

Carbonate

CO3 2-

Perchlorate

ClO4-

Chlorate

ClO3-

Chlorite

ClO2-

Hypochlorite

ClO-

What is atomic radius?

size of an atom