CHEM 86.1 UNIT 1: ATOMS AND THEIR QUANTITATIVE STUDY

Elements

What is the simplest type of matter?

Compounds

Consist of two or more different elements that are bonded chemically.

Mixtures

Consists of two or more substances (elements and/or compounds) that are physically intermingled, not chemically combined.

Mass Conservation

Total mass of substances does not change during a chemical reaction

Law of mass conservation

Definite Composition

No matter what its source, a particular compound is composed of the same element in the same parts (fractions) by mass.

proportions, source

The ___ of elements for the same compound is same no matter what its ___.

Multiple Proportions

If element A and element B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers

ratios of small whole numbers

The law of multiple proportions tells us that in two compounds of the same elements, the mass fraction of one element relative to the other element changes in increments based on ___

John Dalton

___: In 1808, presented his atomic theory of matter.

atoms, created or destroyed

All matter consists of ___, tiny indivisible units of an element that cannot be ___. (This derives from the “eternal, indestructible atoms” proposed by Democritus more than 2000 years earlier and reflects mass conservation as stated by Lavoisier.)

converted

Atoms of one element cannot be ___ into atoms of another element. In chemical reactions, the atoms of the original substances combine to form different substances. (This rejects the alchemical belief in the magical transmutation of elements.)

mass, properties, element

Atoms of an element are identical in ___ and other ___ and are different from atoms of any other ___. (This contains Dalton’s major new ideas: unique mass and properties for the atoms of a given element.)

chemical combination, ratio, definite composition

Compounds result from the ___ of a specific ___ of atoms of different elements. (This follows directly from the law of ___)

Mass Conservation

Atoms cannot be created or destroyed (postulate 1) or converted into other types of atoms (postulate 2). Therefore, a chemical reaction cannot possibly result in a mass change because atoms are just combined differently.

Definite Composition

A compound is a combination of a specific ratio of different atoms (postulate 4), each of which has a particular mass (postulate 3). Thus, each element in a compound must constitute a fixed fraction of the total mass.

Multiple proportion

Atoms of an element have the same mass (postulate 3) and are indivisible (postulate 1). The masses of element B that combine with a fixed mass of element A must give a small, whole-number ratio because different numbers of B atoms combine with each A atom in different compounds.

Cathode Rays

To discover the nature of an electric current, some investigators tried passing it through nearly evacuated glass tubes fitted with metal electrodes

(1) Ray bends in magnetic fielld - Consists of charged particles (2) Ray bends toward positive plate in electric field - Consists of negative particles

(3) Ray is identical for any cathode - Particles found in all matter

What are the observations and conclusions of the Cathode Rays experiment?

J. J. Thomson

In 1897, the British physicist ___ (1856–1940) measured the ratio of the mass of a cathode ray particle to its charge

Millikan’s oil-drop experiment

___: In 1909, the American physicist Robert Millikan (1868–1953) measured the charge of the electron

X-ray, oil droplets, positively charged plate, magnetic field, mass

In Millikan’s oil drop experiment, __________ ejects electrons from the gas molecules in air, and these electrons become attached to __________. The negatively charged oil droplets then fall through the hole in the __________. By turning off the __________, Millikan measured the __________ of electrons based on the rate of fall of the oil droplets.

plum-pudding

Thomson proposed his “___” model—a spherical atom composed of diffuse, positively charged matter with electrons embedded in it like “raisins in a plum pudding.”

-1.60 x 10-19 C, -1.76 x 108 C/g , 9.10 x 10-28 g

e - charge =___

Thomson’s charge/mass of e- = ___

e - mass = ___

CONST03

In calculator, e - mass is saved as ___

Rutherford’s Gold-foil experiment, Ernest Rutherford

___: In 1910, New Zealand–born physicist ___ (1871-1937) tested the Plum-Pudding model

nucleus, electron, 1840x

✔atoms positive charge is concentrated in the ___

✔proton (p) has opposite (+) charge of (-) __

✔mass of p is ___ mass of e- (1.67 x 10- 24 g)

Chadwick’s experiment, James, neutron, nucleus

____: After more than 20 years, in 1932, ___Chadwick (1891–1974) discovered the ___, an uncharged dense particle that also resides in the ___

1.67 x 10-24 g

n mass ~ p mass = ___

CONST02, CONST01

In calculator, n 0 mass is saved as__ and p + mass is ___

nucleus, protons

Due to the small mass of electron, the total mass of an atom must come from the ___ but not from the ___ alone

Atom

an electrically neutral, spherical entity composed of a positively charged central nucleus surrounded by one or more negatively charged electrons.

nucleus

An atomic ___ consists of protons (p+ )and neutrons (n 0 ).

protons, electrons

An atom is neutral because the number of ___ in the nucleus equals the number of ___ surrounding the nucleus.

Atomic Number

number of protons in nucleus

Mass Number

number of protons + number of neutrons = atomic number (Z) + number of neutrons

Atomic Symbol

Element symbol based on its English, Latin or Greek name

Isotopes

Atoms of the same element with different number of neutrons in the nuclei.

Cation

A neutral atom that loses an electron; Ion with a positive charge.

Anion

: A neutral atom that gains an electron; Ion with a negative charge

Wavelength (lambda, λ)

Distance between identical points on successive waves

Amplitude

Vertical distance from the midline of a wave to the peak or through.

Frequency (nu, ν)

number of waves that pass through a particular point in 1 second (Hz= 1 cycle/s)

electromagnetic waves

In 1873, Maxwell proposed that visible light consists of ____.

Electronic radiation

____ is the emission and transmission of energy in the form of electromagnetic waves.

3.00 x 108 m/s

Speed of light (c) in vacuum = ___

speed, frequencuy, wavelength

All waves of electromagnetic radiation travel at the same ___ through a vacuum but differ in ___ and, therefore, ___.

All electromagnetic radiation

λ · ν = c

Blackbody Problem

___: Changes in the intensity and wavelength of emitted light as an object is heated are characteristic of blackbody radiation, light given off by a hot blackbody

Quantum Theory

___: In 1900, Max Planck (1858-1947) assumed that hot, glowing objects could emit (or absorb) only certain quantity of energy (quantum).

h x v

E = ___

Planck’s Constant (h), CONST06

___ = 6.62606957 x 10-34 J·s = 6.626 x 10-34 J·s (In calcu saved as ___)

Photoelectric effect

___: When monochromatic light of sufficient frequency shines on a metal plate, a current flows.

presence of threshold frequency, absence of time lag

It was thought that the current arise because light transfer energy that frees electrons from the metal surface. However, it offers two confusing features: the ___ and the ___.

Einstein

___ proposed that light is a particulate, quantized into tiny “bundles” of energy called photons.

Presence of threshold frequency

___: A photon of a certain minimum energy must be absorbed to free an electron from the surface.

Absence of time lag

___: As long as the threshold frequency is met, electrons immediately ejected.

(quantized) energy values

Electrons (e- ) can only have specific ___

lower

Light is emitted as e - moves from one energy level to a ___ energy level

Erwin, quantum-mechanical model of the H atom

Quantum Mechanics: In 1926, ___ Schrödinger (1887–1961) derived an equation that is the basis for the ___

distance of e - from the nucleus

n = principal quantum number = 1, 2, 3, 4, … = ___

shape of the “volume” of space that e - occupies

l = angular momentum quantum number = 0, 1, 2, 3, …, n-1 = ___

s, sharp, p, principal, d, diffused, f, fundamental

l = 0 = ___ = ___

l = 1 = ___ = ___

l = 2 = ___ = ___

l = 3 = ___ = ___

orientation of the orbital in space

ml = magnetic quantum number = -l, …, 0, …, +l

= ___

spin quantum number

ms = ___ = -1/2 or +1/2 = orientation of the orbital in space

Pauli’s Exclusion Principle

___: no two electron in an atom can have the same four quantum numbers

shell

electrons with the same value of n

subshell

electrons with the same value of n and l

orbital

electrons with the same values of n, l, and ml

2

An orbital can hold how many electrons?

1 possible orbital

s orbital – ___

3 possible orbitals

p orbital - ___

5 possible orbitals

d orbital - ___

7 possible orbitals

f orbital - ___

Hund’s rule

___: “If more than one orbital in 1 a subshell is available, electrons will fill empty orbitals before pairing up.”

Electron Configuration

distribution of electrons in an atom

Aufbau’s Building-up Principle

___: Electrons must completely fill up lower energy levels before filling up the next higher energy level

Valence electrons

___: Electrons occupying the outermost shell

Differentiating Electron

___: Last entering electron in the configuration of an element

Isoelectronic

___: atoms or ions of different elements that have the same electronic configuration

representative elements

For ___, elements form ions to become isoelectronic with the nearest noble gas

transition metals

For ___, electrons from the outermost shell are the first to be removed. (“First In, First Out”)

half-filled or completely filled

Exceptions: There are atoms gain extra stability when their d subshells are ___.

Diamagnetism

___: slightly affected by magnet; all electrons are paired

Paramagnetism

___: greatly affected by magnet: contains an unpaired electrons

paramagnetic

2 unpaired electrons = ___

diamagnetic

all electrons are paired = ___