Chemistry 141: Week One

Element

a pure substance that is unable to break down

atom

the basic building block of matter that makes up everything in the universe

Molecule

a group of two or more atoms stuck together by chemical bonds

compound

a substance made of two or more different chemical elements that are joined together by chemical bonds

extensive property

a physical property of matter that depends on the amount of substance present

• i.e. mass, volume, length/size, total energy/heat content, number of moles

intensive property

a physical property of matter that does not depend on the amount or size fo the substance present

• i.e. density, temp, boiling and melting points, and color

Physical property

a characteristic of matter that you can observe or measure without changing the identity of the substance

• i.e. how heavy an object is compared to its size

physical change

a change in the appearance, shape, size, or state of matter that does not create a new substance or alter its chemical composition

• i.e. melting of an ice cube

chemical change

The process that occurs when one or more substances transform into completely new substances with different chemical compositions and properties

• Burning wood into ash and smoke

Chemical property

a characteristic or trait that describes a substance’s potential or ability to undergo a specific chemical reaction or transformation

• i.e. flammibility

heterogenous mixture

a combination of two or more substances where the composition is not uniform throughout

homogenous mixture

a physical combination of two or ore substances that has a completely uniform composition and appearance throughout

Additional and subtraction using sig figs

when adding or subtracting numbers, round the result to the same number of decimal places as the number with the fewest decimal places

multiplication and division with sig figs

when multiplying or dividing numbers, round the result to the same number of digits as the number with the fewest sig figs (the least value in terms of multiplication and division)

accuracy

how close a measured value is to the true accepted standard value

precision

how close a series of repeated measurements are to each to other

dimensional analysis

Problem-solving technique that uses conversion factors to convert a quantity from one unit of measurement to another, or to check the logical consistency of equations

Leucippus and Democritus

• time: Ancient Greece

• No experiment, just thoughts/ideas

• Conclusion: matter consisted of various combinations of the fair “elements”—earth, wind, fire, and air—and could be infinitely divided

• Corresponding model of atom: ‘atomos’—invisible (small, finite particles`

Dalton

• time: 1819

• Experiment: the combination of elements in chemical reactions

• Conclusion: when two elements react to form more than one compound a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers

• Corresponding model of the atom: a combination of 2 elements such as copper and chlorine into a compound

J.J. Thompson

• time: late 1800’s

• Experiment: an apparatus that consisted of a sealed glass tube with no air and contained two metal electrodes. High voltage-cathode appears

• Conclusion: the cathode ray particles were much lighter than atoms. Particles = attracted by (+) charges and repelled by (-) charges. (Like charges repel and unlike charges attract)

• Corresponding model of the atom: plum pudding

Robert A. Milikan

• time: 1909

• Experiment: oil drop

• Conclusion: The charge 1.6×10 to the negative 9 is the charge of a single electron. The mass of an electron is 9.107 × 10 to the -31 kg

• Corresponding model of the atom: continued extension of the plum pudding model

Rutherford

• time: 1909

• Experiment: used beam of high-speed, positively charged alpha particles produced by radioactive decay of radium; lead block embedded to absorb most of the radiation)

• Conclusion: there must be empty space inside the atom; there must be a nucleus inside the atom

• Corresponding model of the atom: the mode version of an atom to say that contains protons and neutrons

subatomic particle

Electron, neutron, proton

mass in atomic mass units

Dalton (Da).

• proton: 1.00727

• Electron: 0.00055

• Neutron: 1.00866

Charge in electron

Electron is -1.602×10 to the -19

Proton is 1.602 ×10 to the -19

Neutron is 0

mass number

The sum of the numbers of protons and neutrons in the nucleus of an atom

mass of an isotope

the mass of a specific isotope for the element

average atomic mass

the mass of an element shown in a periodic table or listed in a table of atomic masses that is weighted. The equation is equal to the sum of each individual isotope’s mass multiplied by its fractional abundance

molecular or covalent bonds

when the valence electrons are shared equally between other elements

Marie and Pierre Curie

isolated of radioactive elements. Certain elements emit high energy radiation

• first x-ray image!

Atomic number

the number of protons present in every atom of that element

isotopes

All have the same number of protons different number of neutrons