AP Chem chs. 1,2,3

what are the rules for counting significant figures?

1. nonzero numbers are always significant 2. zeros between nonzero numbers are always significant 3. all final zeros to the right of the decimal point are significant 4. placeholder zeros are not significant 5. counting numbers and defined constants have an infinite number of significant figures

what happens in a chemical reaction and why is mass conserved in a chemical reaction?

a chemical reaction involves reorganization of atoms; bonds are broken between atoms in reactants, and new bonds are formed in products; the number and types of atoms do not change, atoms are conserved and mass is also conserved

what is the law of definite proportion?

a given compound always contains exactly the same proportion of elements by mass

accuracy

agreement of a particular value with the true value

how are atoms of hydrogen identical to each other and how can they be different from each other?

all atoms of hydrogen have one proton; isotopes have different number of neutrons; neutral atoms have same amount of protons and electrons

what is a qualitative observation?

an observation you make that expresses what makes something like it is

ion

atom or group of atoms that has a net positive or negative charge

what are covalent bonds?

bonds that form between atoms by sharing electrons. resulting collection of atoms is called a molecule

what are ionic bonds?

bonds that form due to force of attraction between oppositely charged ions.

what is the difference between chlorine and chloride ion? a sodium atom and ion?

chlorine has 17 electrons whereas chloride has 18 electrons (ion has one more electron) sodium atom has 11 electrons, ion has 10 electrons (ion has one less electron)

what are the contributions of Mendeleev?

created first periodic table (predicted properties of new elements)

precision

degree of agreement among several measurements of the same quantity

write the most common guidelines to determine significant figures,

digits 1-9 are significant zeros between 1-9 are significant zeros after the decimal and after significant figures are significant

what are the contributions of JJ Thompson?

discovered electrons (cathode ray experiment)

what are the contributions of Ernest Rutherford?

discovered nucleus (gold foil experiment)

what are the contributions of Henry Becquerel?

discovered radioactivity

what are the contributions of Democritus?

he came up with the idea of atoms

how are atoms of hydrogen different from atoms of helium? how can hydrogen atoms be similar to helium atoms?

hydrogen atoms always have one proton, and helium atoms always have two protons. assuming neutral atoms, also hydrogen has one electron and helium has two electrons

what do significant figures help do?

includes all known digits plus one estimated digit in calculations, determines the amount of rounding to be done based on the precision of the measurements

Dalton assumed that all atoms of the same element were identical in all their properties. explain why this assumption is not valid.

isotopes= atoms of the same element with different number of neutrons, therefore different masses

what is the assumed uncertainty in a number (unless stated otherwise)? the uncertainty of a measurement depends on the precision of the measuring device. explain.

it is assumed to be +-1 it is based on the amount of significant figures on the instrument

how do you add/subtract with sig figs?

look for measurement with fewest number of decimal places the answer can have only as many sig figs to the right of the decimal point as the least precise measurement

how do you multiply/divide with sig figs?

look for measurement with fewest sig figs answer can only have as many sig figs as the least precise measurement (fewest sig figs)

atomic mass

mass of protons and neutrons

what are the SI units for mass, length, and volume?

mass= kilogram length=meter volume=m3 (cubed)

atomic number

number of protons

what is the scientific method?

process that lies at the center of scientific inquiry

the atom can be broken down into smaller parts. what are the smaller parts?

protons, electrons and neutrons

what is a measurement?

quantitative observation consisting of two parts

atom

smallest part of an element that is still that element

mass number

sum of protons and neutrons (round mass to whole number)

how do you go from grams to milligrams?

there are 1000 miligrams in one gram

molecule

two or more atoms joined and acting as a unit

what is a digit that must be estimated called?

uncertain

how is water different from hydrogen peroxide even though both compounds are composed of only hydrogen and oxygen?

water is always one gram of hydrogen for every 8 grams of oxygen present, whereas hydrogen peroxide is always one gram of hydrogen for every 16g of oxygen present; they are distinctly different compounds

what is the law of multiple proportions?

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