chem ch 2

substances

Element (Single atom)

• Molecule (≧ 2 atoms, same or

different)

• Compound (≧ 2 different

atoms)

element

single atom, a pure substance that cannot be broken down

molecules

2 or more atoms, same or different

compound

2 or more atoms that are different

can be broken down by chemical reaction

homogeneous mixture

no visible boundaries because the components are mixed as individual atoms

also known as solution

heterogenous mixture

has one or more visible boundary between components

mixture vs compound

mixture: a physical mixture of elements that can be separated without chemical change

compound: reacted chemically to form a new compound, elements cannot be separated by physical means

methods of separating mixtures

filtration

crystallization

distillation

chromatography

filtration

separates a solid from a liquid

• based on differences in particle size

ex: separating sand from water

crystallization (solubility)

based on differences in solubility

a solute dissolves in hot solvent, impurities will remain in the solution as it cools

ex: taking sugar water and making sugar crystals

distillation

based on differences in volatility (boiling point)

the more volatile component vaporizes first, condenses, and is collected

simple distillation: large boiling point differences

fractional distillation: small boiling point differences

ex: solution of chlorine and water is boiled, the water vaporizes and is collected separately, the chlorine remains behind

chromatography

based on differences in solubility/affinity

separates a mixture because different substances travel at different speeds through a material, some are more stationary, some are more mobile

4 parts of daltons atomic theory

• postulate 1. all matter consists of atoms that cannot be created or destroyed

postulate 2. Atoms of one element CANNOT be converted into atoms of another element.

• postulate 3. atoms of an element are identical in mass and properties, different from other elements

postulate 4. Compounds result from the chemical

combination of a SPECIFIC RATIO of atoms of different

elements. In simple whole-number ratio. ex: C O2

• 
  

law of mass conservation

The total mass of substances present does not change

during a chemical reaction.

Atoms cannot be created or destroyed.

Atoms can not be converted into other types of atoms.

During a chemical reaction the same atoms are present but in

different combinations; therefore there is no mass change

overall.

law of definite composition

No matter the source, a compound's elements occur in the same proportion by mass.

Atoms are combined in compounds in specific ratios.

Each atom has a specific mass.

Each element constitutes a fixed fraction of the total mass in a compound.

This law compares elements in one compound.

Law of Multiple Proportions

This law compares different compounds made of the same elements

If elements A and B react to form two compounds, the

different masses of B combining with a fixed mass of A

result in a small whole-number ratio

Atoms of an element have the same mass.

Atoms are indivisible.

When elements combine to form a compound, their atoms

always combine in fixed, small whole-number ratios

how was the electron discovered

J.J. Thomson discovered the electron

using cathode ray tube experiments.

it was discovered first

how was the proton discovered

Ernest Rutherford discovered the nucleus

in 1911 and established protons as fundamental

constituents in 1919.

it was discovered second

how was the neutron discovered

James Chadwick completed the modern

model by discovering the uncharged neutron.

discovered last

what did thomson discover

the existance of electrons and they are present in all matter

came up with the plum pudding model : pudding is possitive, plums are the negative electrons

millikan’s oil drop method

fine mist of oil is sprayed into a chamber of air

oil droplets fall through hole in positively charged plate

electrically charged plates influence the droplets motion

X-rays knock electrons from air molecules,

which stick to falling droplets.

Combining Charge and Mass-to-Charge Ratio

Millikan measured the charge of single electron.

By pairing Thomson's measured mass-to-charge ratio with Millikan's

charge discovery, physicists calculated the fundamental mass of a

single electron

Rutherford's Alpha Scattering Experiment

The Atomic Nucleus Discovery

The Hypothesis: Under J.J. Thomson's Plum-Pudding model,

positive charge is highly diffuse. Fired α-particles (Helium nuclei

He2+) should pass directly through gold foil with almost no

deflection.

The Result: While most particles indeed passed straight through,

a tiny fraction underwent major, sharp deflections.

The Model: Rutherford concluded that the atom has its positive

charge concentrated in a tiny, massive central nucleus

Rutherford’s Conclusions

An atom is mostly empty space occupied by electrons.

o The center of an atom contains a nucleus.

o There’re tiny (+) particles reside in the nucleus, called Protons.

The Modern Atomic Scale

The atom is an electrically neutral, spherical entity composed of a positive central nucleus (made of protons and neutrons) surrounded by negative electrons.

how much of an atom’s mass is from the nucleus

99.97%

atomic number

number of protons

atomic mass

number of protons and neutrons

how do you find the number of electrons in an element using the periodic table?

it should be the same as the atomic number because in a neutral atom the number of protons is= to the number of electrons

where are the metals at on the periodic table

red, orange, light green

good electrical conductors. Tend to lose

electrons in chemical reactions and became cation

where are the nonmetals at on the periodic table

Upper right corner; poor thermal conductors. Tend to gain

electrons in chemical reactions and became anions

blue, purple

where are the metalloids (semimetals) at on the periodic table

Form staircase separating metals and nonmetals.

dark green

where are the Nobel Gases (inert gases ) at on the periodic table

right most column (purple)

from top to bottom the atomic radius (number of electron shells) increases/decreases

increases, each new row adds a new layer of electrons

from top to bottom atomic size (the size of the particles) increase/decrease

increase, the size of the particles get larger as you go down the columns

from left to right atomic size (the size of the particles) increase/decrease

decrease

the largest atom in the periodic table would be in which direction

lower left corner

standard notation for elements

atomic mass (protons + neutrons)

______________E

number of protons (atomic number)

why do we use standard notation for elements

esigned to represent specific individual isotopes. (differences in neutrons)

ion

an atom (or group of atoms) with one or more positive/negative charges

• when an atom gains or loses an electron

• when the number of protons isn’t equal to the number of electrons

are all isotopes man made?

Some isotopes are naturally occurring, and some are synthetic (man-made)

how many isotopes do elements have?

Elements can have a multitude of isotopes; each with a different mass number.

are isotopes stable?

Some isotopes are stable, and others are unstable and undergo nuclear decay.

can you determine the identity of an isotope by looking at the periodic table?

no

chemical properties of an element are mostly determined by

the number of electrons

do isotopes have the same/different chemical behavior as their element

near identical

atomic mass of isotope equation

atomic mass= AMUa(%abu a/100%)+ AMUb(%abu b/100%) + . . .

in a compound are the elements in a fixed mass ratio?

yes

ionic bound

usually between a metal and nonmetal when metal transfers electrons to nonmetal

the process of transferring electrons results in the formation of two different ions that are attracted to each other, making them stick together, bonding them

covelent bond

results from sharing of electrons

crystal

ions pack together to maximize attraction

metals tend to lose electrons until

they have the same number of elctrons as the nearest noble gas

non metals tend to gain electrons until

they have the same number of elctrons as the nearest noble gas

the noble gas rule

ions typically form by losing or gaining electrons to match the count of the nearest noble gas (last column of the periodic table on the right)

what is the z value in standar form

the number of protons

monatomic ion

The charged particle formed from a single atom by

gaining or losing electrons. Such as Cations from metal

atoms, Anions from nonmetal atoms

Polyatomic Ion

A group of covalently bonded atoms that possesses a

net overall positive or negative charge. Operates as a

single unit in reactions (e.g., Carbonate, ).

molecular elements

Certain elements occur naturally not as single atoms, but

as multi-atom molecules: such as the followings

diatomic molecules

elements that are never alone in nature and always come in twos

H2

N2

O2

F2

Cl2

Br2

I2

tetratomic molecule

elements that are never alone in nature and always come in fours

P4

octatomic molecules

molecules that always come in 8s

S8

Se8

discrete units v.s continuous network

discrete: particles exist as seperate, individual groups

ex: H2O is an individual water molecule

continuous network: atoms are connected in a huge repeating structure rather than forming separate molecules

ex: a diamond

ion

a single atom or covalently bonded group of atoms that

has an overall electrical charge

gained or lost an electron

CHEMICAL FORMULA

A chemical formula consists of element symbols with numerical subscripts.

• A chemical formula indicates the type and number of each atom present in the

smallest unit of a substance.

for all ionic compounds, the name and formula lists the first, and the ___ second

cation, anion

in a binary ionic compound both the cation and the anion are monatomic/polyatomic

monatomic

many metal names end in

-ium

the anion is named by adding the suffix __ to the root of the nonmetal name

-ide

ex: calcium and bromine form calcium bromide

the column with a +1 charge on PT

left most colum

the column with a +2 charge on PT

2nd leftmost column

the column with a +3 charge on PT

6th column from the right

the column with a -3 charge on PT

4th column from the right

the column with a -2 charge on PT

3rd column from the right

the column with a -1 charge on PT

2nd column from the right

the column with a 0 charge on PT

rightmost column

Formula writing for ionic compounds

1. Cation first and anion second

2. Compound has zero net charge, so charges need to be balanced

3. Subscript refers to the element symbol preceding it

4. Subscripts need to be reduced to the smallest whole number

ex: Ca²+ and Br^1-

CaBr2

because calcium has a positive charge of 2 and Bromine has a charge of -1 you need 2 bromine to balance the equation

know lewis dot diagrams

yea

know ur roman numerals

yea

When Polyatomic is cation how do you name stuff

Polyatomic name + base name of non-metal + “ide”

Example: NH4F, Ammonium fluoride

When Polyatomic is anion how do you name stuf

Name of metal/cation + polyatomic name (not ide)

Example, Mg(NO3)2, Magnesium Nitrate

a lot of them will have ate but not all, ate is not the key component here, the polyatomic name itself decides the suffix

Oxyanions

Most polyatomic ions are oxyanions, means the nonmetal element is bonded to one or more oxygen atom.

always has a negative charge

oxygen is the 2nd most electronegative element making it very reactive

Ate= extra oxygen, usually >or= 3

ite= less oxygen, usually < or =3