Chem 1 Pearson ch. 2

Dalton’s Atomic Theory

all matter is composed of atoms, atoms of the same element are identical, atoms combine to form compounds, chemical reactions rearrange atoms, atoms of different elements are unique

law of conservation of mass

in a chemical reaction matter is neither created nor destroyed

law of definite proportions

all samples of a given compound have the same proportions of their constituent elements

(16.0g O / 2.0g H = 8:1)

law of multiple proportions

when 2 elements form two different compounds, the ratios of the masses can be expressed as a ratio of whole numbers

(O:C in CO2 = 2.67:1, O:C in CO = 1.33:1 → 2.67/1.33 = 2)

particles in the nucleus

proton, neutron

particles around nucleus

electrons (electron cloud)

electrostatic forces

electrical charge & attractive & repulsive forces in atoms

electric field

the area around a charged particle where electrostatic forces exist

plum pudding model

later disproved by Rutherford Gold Foil Experiment

radioactivity

the emission of small energetic particles from the core of certain unstable atoms

nuclear theory of the atom

most of at atom’s mass and positive charge are in the nucleus, most of an atom’s volume is empty space where electrons are dispersed, #electrons = #atoms

proton

+1, defines the element

neutron

0

electron

-1

atomic number (Z)

the number of protons in a nucleus

isotope

same number of protons, different number of neutrons

Dalton corrections

isotopes (all atoms do not have the same mass and not all elements are identical), atoms are divisible (proton, neutron, electron)

mass number (A)

#protons + #neutrons

A notation example

C-12 has 6 protons, 6 neutrons, and a mass number 12

can also be written as carbon-12

neutral atom

equal #electrons and #protons

ions

charged particles that gain or lose electrons

cation

ions that lost electrons

(ex. Li → Li⁺ + Li^-)

anion

ion that gained an electron

(ex. F + 1e^- → F^-)

periodic law

when the elements are arranged in order of increasing mass, certain sets of properties recur periodically

metals

good conductors, malleable, ductile, shiny, lose electrons in chemical reactions

nonmetals

poor conductors, not malleable, not ductile, gain electrons during chemical rxns

metalloids/semi-metals

semiconductors, mixed properties

main group elements

properties tend to be predictable based on position in periodic table

transition elements/transition metals

properties tend to be less predictable based on location in periodic table

main group elements in chemical rxns

tend to form ions that have the same # electrons as the nearest noble gas

1 amu

mass of 1/12th of 1 C-12

1 mol

6.02214(10²³) (Avogadros number), the # of atoms in 12g of pure C-12

molar mass

1 mol of atoms of an element, molar mass in g/mol = atomic mass in amu

g to mol

mass/molar mass

moles to particles

(moles)(Avogadros number)

particles to moles

particles/Avogadros number

moles to grams

(moles)(molar mass)

calculate atomic mass

(fraction of isotope n)(mass of isotope) + (fraction of isotope n)(mass of isotope) + …

1A

+1, alkali metals (reactive)

Note: H is sometimes not considered an alkali metal, but it still has a predictable +1 charge

2A

2+, alkaline earth metals, fairly reactive

3A

3+, boron family, remember Al3+ as primary example, lower elements can have different properties

5A

3-, remember N3- as primary example

6A

2-

7A

-1, H can be here, halogens, very reactive non-metals

8A

noble gases