GEN CHEM 1

THE TRIPLET REPRESENTATION

Macroscopic, microscopic, symbolic

Pure substances

an be an element or a compound

Element

the simplest type of substance with unique physical and chemical properties

• consists of only one type of atom

Compound

a substance composed of atoms of two or more elements that are chemically combined

• properties are different than those of its elements

Molecule

a structure that consists of two or more atoms that are chemically bound together and thus behaves as an independent unit

• Can be elements or compounds

Mixture

a group of two or more elements and/or compounds that are physically intermingled

Heterogenous Mixture

has one or more visible boundaries between the components

Homogenous Mixture

as no visible boundaries because the components are mixed as individual atoms, ions, and/or molecules

• Is also called a solution

Aqueous Solution

Solutions in which water is the solvent

Chemical Property

A property that is that is associated with a change in chemical composition

• Examples: flammability, pH

Chemical Change

A change of matter that results in a change in its chemical composition

• Examples: rusting of metal, lighting a match, taking antacid for heartburn

Physical Property

A property that is that is not associated with a change in chemical composition

• Examples: physical state/phase, density, color

Physical Change

A physical change occurs with a change in state/phase

• Examples: melting ice, boiling water, tearing paper, sanding wood

Solid

has a fixed shape and volume

• May be hard or soft, rigid or flexible

Liquid

as a varying shape that conforms to the shape of the container, but a fixed volume

• Has an upper surface

Gas

has no fixed shape or volume and therefore does not have a surface

Metric Prefixes

Tetra 10^12. deci 10^-1

Giga 10^9 centi 10^-2

Mega 10^6 milli 10^-3

Kilo 10^3 micro 10^-6

Hecto 10^2 nano 10^-9

Deca 10^1 pico 10^-12

7 Base SI Units

Length- meter (m)

Mass- kilogram (kg)

Temperature- kelvin (K)

Time- second (s)

Electric Current- ampere (A)

Amount of Substance- mole (mol)

Luminous Intensity- candela (cd)

Derived Units

Volume- m³

Density- kg/m³, g/cm³

• Gases- g/mL

Accuracy

how close a measurement is to the true value

Precision

how close repeated measurements are to each other

Significant Figures

Recorded digits (including the estimated one) of a measurement

• They reflect how “certain” (precision) we are in the measurement value and help us know how “correct” (accuracy) that value is

• The last digit recorded for a measurement is always estimated

• The more digits a number has, the greater certainty we have in its value

Exact Number

A number with no uncertainty in its value

• 1 ft is exactly 12 in

• 1 in is exactly 2.54 cm

• 1 kg is exactly 103 g

-Contain an infinite number of significant figures

Non Exact Number

Quantities derived from measurements other than counting that ALWAYS have a certain level of uncertainty

• Due to the practical limitations of the measurement process

• The number of a measurement must be reported to indicate its uncertainty

• The temperature outside (e.g., 72°F)

• Your height or weight

• The time it takes to get to school or work

• The speed of a car

Non Zeros

These are always counted as significant in reported measurements

Zeros

These are sometimes significant and only in these cases:

• At the trailing end of the number AND a decimal is explicitly written

• That are “captive” between non-zeros

Unit Conversions

use a method called the Factor- Label Method

• Utilizes ratios of equivalent units called conversion factors

Scientific Formulas

use mathematical equations to describe the relationships between properties

Dimensional Analysis

The general process of treating units as mathematical quantities in a calculation

Conversion Factor

is a ratio between equivalent measurements each expressed in different unit

Factor Label Method

is a blueprint for unit conversions that utilizes conversion factors to guide the cancellation of units

Postulates of Dalton’s Atomic Theory (1)

All matter consists of atoms; tiny indivisible particles of an element that cannot be created or destroyed

Postulates of Dalton’s Atomic Theory (2)

Atoms of one element cannot be converted into atoms of another element

Postulates of Dalton’s Atomic Theory (3)

Atoms of an element are identical in mass* and other properties but are different from the atoms of any other element

Postulates of Dalton’s Atomic Theory (4)

Compounds result from the chemical combination of a specific ratio of atoms of different elements

The Law of Conservation of Mass

Matter cannot be created or destroyed

The Law of Constant Composition

A specific compound is always composed of the same elements in the same mass percents

The Law of Multiple Proportions

If elements A and 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

Atomic Theory Today

The nucleus consists of protons and neutrons

• The nucleus contributes 99.97% of the atom’s mass but occupies only about 1 quadrillionth of its volume

• The nucleus diameter is about 20,000 times smaller than the diameter of the atom

Atomic Number

The number of protons in the nucleus of an atom

• Its value determines the identity of the atom

Neutral Atoms

Means the total positive (+) charge = total negative (-) charge

• # of p+ = #e-

• The atomic number (Z) also indicates the # of e–

The Periodic Table

Increasing atomic number (Z) order

• Groups: vertical columns that contain a “family” of elements

• Periods: horizontal rows that display a predictable repeating pattern of chemical properties

Isotopes

are atoms that have the same # of p+ but a different # of n0

• Have the same atomic number (Z) but a different mass number (A)

• Are atoms of the same element

Ion

is an atom (or molecule) that has lost or gained one or more electrons

Cation

Positively charged ion

Anion

Negatively charged ion

Atomic Mass

Is the weighted average of all the masses of isotopes present in a natural sample

• Reported on the periodic table

Chemical Formula

consists of element symbols, numerical subscripts, and sometimes parenthesis

• Indicates the type and number of each atom/ion present in the smallest unit of a substance

7 Diatomic Elements

Hydrogen

Nitrogen

Oxygen

Fluorine

Chlorine

Bromine

Iodine

Polyatomic Elements

Phosphorous- 4

Sulfur- 8

Selenium- 8

Chemical Formula Examples (3 Models)

Structural Formula

Ball and Stick Model

Space filling Model

Empirical Formula

indicates the smallest whole-number ratio between the atoms (or ions)

Molecular Formula

Indicates the actual numbers of atoms (or ions) in a molecule

The Mole- Avogadro’s Number

the amount of a substance that contains the same number of entities as there are atoms

Formula Mass

• Sometimes called molecular mass or formula weight

• Sum of atomic masses

Molar Mass

Relates one mole of a substance to its formula mass

• Numerically equal to the formula mass

• Units are grams per mole, g/mol

Mass-Moles-Atoms

Electromagnetic Radiation Spectrum

Wavelength and Frequency relationship

Inversely proportional to each other through the speed of light

Matter (particles)

Comes in chunks you can hold & weigh

• Its quantity can be changed piece by piece

• Moves in specific paths

Energy (waves)

• Is massless

• Its quantity changes on a continuous spectrum

• Light energy travels in disperse waves

The Particle Nature of Light (3 Exceptions)

Blackbody Radiation

The Photoelectric Effect

Atomic Emissions

Blackbody Radiation

when a solid object is heated to high temps, it gives off electromagnetic radiation

• Example: an incandescent lightbulb

The Photoelectric Effect

when sufficient frequencies of light shines on a metal plate, a current flows

• Example: solar panels

Atomic Emissions

when atoms are exited by energy they emit radiation with discrete wavelengths and not in a continuous spectra.

• Example: Neon signs

Quantum Theory

the energy of a small particle is quantized – it occurs in fixed packets (photons) rather than being a continuous spectrum

• Quarters, rungs on a ladder

Photon

A quantized “packet” of electromagnetic radiation

• The energy is directly proportional to its frequency through Planck’s constant.

• Has no mass and at the speed of light in a vacuum

The Particle Nature of Light

A small particle changes its energy by emitting or absorbing one or more photons of light

• The energy that of the emitted or absorbed photon is equal to the difference in the energy states

Wave-Particle Duality

Light exhibits this:

• It travels as an electromagnetic wave, described by wavelength, and frequency

• It transfers energy in discrete packets called photons, whose energy depends on frequency

• The specific behavior of light that is observed depends on how we interact with it

The Early Atomic Model

An atom consisted of tiny dense nuclei surrounded by lighter and even tinier electrons continually moving about the nucleus

• This description was incomplete, since an electron moving in an elliptical orbit would be accelerating and emitting radiation

The Bohr Model

Electrons occupy specific "orbits” around the nucleus, each corresponding to a fixed energy level.

• Electrons can "jump" between these energy levels, but they cannot exist between them

• An electron emits or absorbs a photon if it moves to a different orbit

The Quantum Staircase

• The lowest energy orbit is called the ground state

• All other energy orbits are called excited states

• An electron:

• absorbs a photon if it moves from a lower energy orbit to a higher energy orbit

• emits a photon if it moves from a higher energy orbit to a lower energy orbit

Fireworks and Neon Signs

These glow with distinct colors because electrons absorb energy (from heat or electricity) and, when they drop between energy levels, they emit specific wavelengths of visible light

Atomic Spectra

Visible light will refract through a prism and create a continuous spectra of colors – called a rainbow

• A sample of a pure gaseous element does not emit a continuous spectra of light when it is exited (energized)

• are like an element’s fingerprints – they are unique for each element

Spectral Lines of Atomic Hydrogen

Ultraviolet series n2=1

Visible Light series n2=2

Infrared series n2=3