(Chem 200) 02- Atoms And Elements

Front 1

atmos (greek) =

Back 1

invisible

Front 2

Scanning tunneling microscopy (STM):

Back 2

- discovered by Gerd Binning and Heinrich Rohrer.

- technique that can image (make a visual representation of), and even move, individual atoms and molecules.

- works by moving an extremely sharp electrode (a conductor through which electricity can enter or leave) over a surface and measuring the resulting tunneling current.

Front 3

Tunneling Current:

Back 3

the electrical current flows between the tip of the electrode & the surface even though the two are not in physical contact.

Front 4

atom:

Back 4

smallest identifiable unit of an element.

Front 5

Law of conservation of mass:

Back 5

by Antonine Lavoisier

"in a chemical reaction, matter is neither created nor destroyed"

Front 6

Law of Definite Proportions:

Back 6

by Joseph Proust

"All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements."

Front 7

Law of multiple Proportions:

Back 7

by John Dalton

"when two elements (call them A & B) form two different compounds, the masses of element B that combines with 1 g of element A can be expressed as a ratio of small whole numbers.

Front 8

Explain the difference between the law of definite proportions and the law of multiple proportions.

Back 8

the law of definite proportions applies to two or more samples of the same compound and states that the ratio of one element to the other in the sample will always be the same. The law of multiple proportions applies to two different compounds containing the same two elements (A and B) and states that the masses of B that combine with 1 g of A are related as a small whole number ratio

Front 9

John Dalton's Atomic Theory:

Back 9

1. each element is composed of tiny, indestructible particles called atoms.

2. All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements

3. atoms combine in simple, whole-number ratios to form compounds

4. atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms change the way that they are bound together with other atoms to form a new substance.

Front 10

Cathode:

Back 10

negatively charged electorde

Front 11

anode:

Back 11

positively charged electrode

Front 12

What did J.J. Thomas Discover?

Back 12

- Found that cathode rays were actually streams of particles with the following properties:
- they traveled in straight lines

- they carried a (-) electrical charge.

- Discovered the electron, (-) charged, low mass particle present within all atoms.

Front 13

Electrical charge:

Back 13

a fundamental property of some of the particles that compose atoms and results in attractive and repulsive forces (electrostatic forces) between them.

Front 14

Millikan's Oil Drop Experiment:

Back 14

- oil was sprayed into fine droplets using an atomizer.

- droplets were allowed to fall through a small hole into the lower portion of the apparatus where they could be viewed with the help of a light source and a microscope.

- during their fall, the drops acquired electrons that had been produced when the air was bombarded with a type of energy called ionizing radiation.

- the negatively charged drops then interacted with the negatively charged plate at the bottom of the apparatus.

- by varying the amount of charge on teh plate, the fall of the drops could be slowed, stopped, or even reversed.

Front 15

Plum-Pudding model:

Back 15

proposed by J.J Thomas

negatively charged electrons were small particles held within a positively charged sphere.

Front 16

What did Ernest Rutherford Discover?

Back 16

- proved the plum-pudding model wrong.

- in the experiment, he directed the positively charged alpha particles at an unltrathin sheet of gold foil.
-Particles were to act as probes of the gold atoms structure.
- what was suppose to happen: speeding probes should pass right though the gold foil with min. deflection since gold atoms were spread throughout the entire vol. of the atom.

- results: a majority of the particles did pass directly thought the foil, but some particles were deflected and some even bounced back.
- realized, the mass & (+) charges of an atom must be concentrated in a space smaller than the atom
** discovered the nucleus***

Front 17

Nuclear Theory:

Back 17

by Rutherford

1. most of the atom's mass and all of its (+) charge are contained in a small core called the nucleus

2. most of the volume of the atom is empty space, throughout which tiny, (-) charged electrons are dispersed.

3. there are as many negatively charged electrons outside the nucleus as there are positively charged particles (protons) within the nucleus, so the atom is electrically neutral.

Front 18

What did James Chadwick discover?

Back 18

the unaccounted mass of an atom was due to the presence of neutrons (neutral particles within the nucleus).

Front 19

Subatomic particles:

Back 19

Front 20

If all atoms are composed of the same subatomic particles, then what makes the atoms of one element different from those of another?

Back 20

- the # of these particles

- the # that is most important for the identity of an atom is the # of protons in its nucleus

- # of protons defines the element

Front 21

Atomic # (Z):

Back 21

# of protons in an atom's nucleus.

Front 22

periodic table:

Back 22

Front 23

Isotopes:

Back 23

atoms with the same # of protons but different # of neutrons.

Front 24

Mass # (A):

Back 24

the sum of the # of neutrons & protons in an atom.

Front 25

How are isotopes often symbolized:

Back 25

Front 26

Ion:

Back 26

charged atom

Front 27

anion:

Back 27

(-) charged ion

Front 28

cation:

Back 28

(+) charged ion.

Front 29

In light of the nuclear model for the atom, which of the following statements is most likely to be true?
(a) the isotope of an atom with a greater number of neutrons is larger than one with a smaller number of neutrons

(b) the size of an anion is greater than the size of the corresponding neutral atom

(c) the size of a cation is greater than the size of the corresponding neutral atom

Back 29

(b) the number of neutrons in the nucleus of an atom does not affect the atom's size because the nucleus is miniscule compared to the atom itself. The number of electrons however, does affect the size of the atom because most of the vol. of the atom is occupied by electrons, and electrons repel one another. Therefore, an anion, with a greater number of electrons, is larger than the corresponding neutral atom.

Front 30

Dmitri Mendeleev discovered:

Back 30

the periodic table.

Front 31

Periodic law:

Back 31

by Mendeleev

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

Front 32

Modern periodic table:

Back 32

Front 33

Metals:

Back 33

- found on the lower left side and middle of the periodic table.

Properties:
- good conductors of heat & electricity

- can be pounded into flat sheets (malleability)

- can be drawn into wires (ductility)

- often shiny

- tend to lose electrons when they undergo chemical changes

Front 34

Nonmetals:

Back 34

- found on the upper right side of the periodic table.

properties:
- some are solids @ room temp. others are liquids or gases.

- poor conductors of heat & electricity

- tend to gain electrons when they undergo chemical changes.

Front 35

Metalloids:

Back 35

- show mixed properties

- some are semiconductors because of their intermediate (& highly temp. dependent) electrical conductivity.

Front 36

Main-group elements:

Back 36

properties tend to be largely predictable based on their position in the periodic table.

Front 37

transition elements (transition metals):

Back 37

properties tend to be less predictable based simply on their position in the periodic table.

Front 38

the periodic table: main-group and transition elements:

Back 38

Front 39

Family (group):

Back 39

columns within the main-group regions of periodic table

Front 40

noble gases:

Back 40

- group 8A elements

- mostly unreactive

Front 41

Alkali metals:

Back 41

- group 1A elements

- all reactive metals

Front 42

Alkaline earth metals:

Back 42

- group 2A elements

- fairly reactive

Front 43

Halogens:

Back 43

- group 7A elements

- very reactive nonmetals

Front 44

A main-group metal tends to what?

Back 44

lose electrons, forming a cation with the same number of electrons as the nearest noble gas

Front 45

A main-group nonmetal tends to what?

Back 45

gain electrons, forming an anion with the same number of electrons as the nearest noble gas.

Front 46

Elements that form ions with predictable charges:

Back 46

Front 47

Atomic Mass:

Back 47

- is listed directly beneath the element's symbol in the periodic table

- represents the avg. mass of the isotopes that compose that element.

Front 48

How to calculate the atomic mass of an atom:

Back 48

Front 49

Avogadro's # =

Back 49

"one mole of anything is 6.022 x 10^23 units of that thing"

Front 50

Converting between # of moles and # of atoms

Back 50

Front 51

molar mass:

Back 51

- the mass of 1 mol of atoms of an element.

- an element's molar mass in grams per mole is numerically equal to the element's atomic mass in atomic mass units.