chem1a midterm 1

chapters 1, 2, an 3, of chemical principles by zumdahl

what is significant when determining sig figs

all non-zeros, interior zeros, trailing zeros (NOT leading zeros)

calculations with sig figs: addition/subtraction

as precise as the least accurate number

calculations with sig figs: multiplication/division

same as the number with the least amount of sig figs

molar mass

the mass of a mole of objects

average atomic mass

the sum of the masses of an atoms isotope, each multiplied by its natural abundance

chemical reaction

a process by which one or more substances are converted into other substances

reactants

starting material

products

substances formed

law of conservation of mass

mass is constant during a chemical reaction

hints for balancing chemical equations

if an element occurs in only one compound on both sides of the equation, balance it first

reaction stoichiometry

the quantitative relationship between the amounts of reactants consumed and those of products formed in chemical reactions as expressed by the balanced chemical equation for the reaction

mole ratios

the stoichiometric relationship between two species in a chemical reaction written as a conversion factor

limiting reagent

the reactant that governs the maximum amount of product that can form

theoretical yield

the maximum quantity (amount, mass, or volume) of product that can be obtained from a given quantity of a specified reactant

percent yield

the fraction of the theoretical yield actually produced

mass percentage composition

the mass of each element as expressed as a percentage of the total mass

empirical formula

tells the relative number of atoms of each element present in the compound

molecular formula

tells the actual numbers of atoms of each element in a molecule

law

a summary of an extensive series of observations

theory

a collection of ideas and concepts used to account for a scientific law

law of conservation of mass

mass of reactants = mass of products

law of definite proportions

when two or more elements combine to form a compound, their masses in that compound are in a fixed and definite ratio

law of multiple proportions

when two elements form a series of compounds, the ratio of the masses of the second element that combined with 1 gram of the first element can always be reduced to small whole numbers

daltons model

defined that each element is made up of tiny particles called atoms, chemical compounds are formed when atoms combine

nucleus

contains protons and neutrons (positively charged, makes up most of the mass of the atom, around 10 -13 cm in diameter)

electron cloud

contains electrons (negatively charged, 10 -8 cm in diameter)

isotope

atoms with the same number of protons but different number of neutrons (same number of electrons as well because they are neutrally charged not ions)

formatting

atomic number (z): number of protons; mass number (a): number of protons + number of neutrons

periodic table

elements are arranged by increasing atomic number, vertical columns are called groups, groups 1,2, and 13-18 are the main group, horizontal rows are called periods

group 1

alkali metals— soft, lustrous, metallic, low melting temperatures, and highly reactive

group 2

alkaline earth metals: similar to group 1 metals but react less vigorously

groups 3-11

transition metals: get their name because these elements are transitional in character between the vigorously reactive metals in the s block and the less reactive metals on the left of the p block

group 17

halogens: all nonmetals, very reactive with alkali metals and alkaline earth metals

group 18

noble gases: colorless, odorless, gasses which are inert due to their full octets

metal

conducts electricity, has a luster, is malleable, and is ductile

nonmetal

does not conduct electricity and is neither malleable nor ductile

metalloid

has the appearance and some properties of a metal but behaves chemically like a nonmetal

cation

positively charged ion, left side

anion

negatively charged ion, right side

pure substance

a substance composed of only one type of element or compound

element

a substance that cannot be broken down into simpler substances

atomic element

elements that exist in nature with single atoms as their base unit

molecular elements

elements that exist in nature as diatomic molecules

compound

a substance composed of two or more compounds in fixed, definite proportions

molecular compound

electrically neutral molecules that are held together by sharing electrons (usually contain only nonmetals)

ionic compounds

ions that are held together by electrostatic attraction which results in an overall electrically neutral compound (usually contains a metal and a nonmetal_

chemical formula

a collection of the chemical symbols and subscripts that show the composition of a substance

general rule for writing chemical formulas

write the most metallic element first: element nearest to the bottom left corner of the periodic table