basic chem atoms and elements

atoms and molecules

what determines how matter behaves?

atoms

• compose all ordinary matter

• “Greek word atomos meaning “indivisible“

Leucipus and Democritus

who wer ethe first to propose the idea that imatter was composed of small, indestructible particles?

“Nothing exists except atoms and empty space; everything else is opinion“

Plato and Aristotle

Who taught matter had no “smallest“ part and that everything was made of various proportions of fire, air, earth, and water?

and was more popular

Dalton’s Atomic Theory

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

2. All atoms of a given element have the same characteristics that

distinguish them from atoms of other elements

3. Atoms of one element cannot change into atoms of another

element

4. Atoms combine in simple, whole-number ratios to form

compounds

atom

• properties of _ determines the property of the matter it composes

• _ is the smallest identifiable unit of an element

• _ are the sub-microscopic particles that constitute the fundamental building blocks of ordinary matter

molecule

two or more atoms joined together (same ot different)

compound

two or more different atoms joined together in a specific ratio and geometric arrangement

opposite

charges that attract each other

Like

charges that repel each other

J.J Thomson

constructed a cathode ray tube , concluding that particles have a negative electrical charge

cathode ray tube

a beam of particles (cathode rays) would travel from the negatively charged electrode (cathode) to the positively charged one (anode)

J.J Thomson

• concluded that his cathode rays must be composed of particles with the following properties:

  • They travel in straight lines

  • It doesn’t matter what type of material they originated from

  • They carry a negative electrical charge

  • He was able to measure the charge-to-mass ratio of the particles

Millikan’s oil drop experiment

• He could vary the strength of the electrical field of the bottom plate, and slow or even reverse the direction of the “falling” negatively charged droplet

→ Remember that like charges repel each other

- Through some complicated measurements and calculations that I’m not getting into, he was able to determine the charges of his droplets

charge of an electron

With Millikan’s work, what do we know about the electron?

mass-to-charge ratio for electrons

With Thomson’s work, what do we know about the electron?

neutral

It was accepted that atoms have a net _ charge

Thomson

Who determined that an electron was:

• Negatively charged

• Much small and extremely lighter than the atom itself

• Present evenly in different kind of substances

Plum-pudding model

Thomson developed _ model where:
  - Electrons floating within a positively charged sphere

• Think of a spherical chocolate chip cookie

• Chocolate chips = electrons

• Cookie = positively charged “sphere”

Ernest Rutherford

• Worked under Thomson

  • Set out to confirm the “plum-pudding” model
    

  • The experiment:

     Use α-particles

     Positively charged

     ~7000 times more massive than an electron

  • Direct α-particles at an ultra-thin sheet of gold foil

  • The idea:

    • All the α-particles should pass right through, with no deviation

    • What happened:

      • Not that lmao

Gold foil experiment

Rutherford’s experiment where Most of the α-particles did pass straight through as predicted

• BUT, some particles were deflected while a few (1 in 20,000) were

actually “reflected”

• Rutherford described this as making as much sense as “firing a 15-

in shell at a piece of tissue paper and it came back and hit you”

Rutherford

• concluded that matter is nothing more than large regions of empty space with VERY small regions of very dense matter

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

Rutherford

• results changed everything, so a new “model” was needed to explain how an atom is composed

• Most of an atom’s mass and all its positive charge is contained in a small core called the nucleus

• Most of the volume of the atom is empty space, throughout which tiny, negatively charged electrons are dispersed

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

James Chadwick

Who discovered the neutron?

Neutrons

• are particles that have about the same mass of a proton, but absolutely no charge

• “Changing” the number of _ will change the mass of the atom, but has no affect on the overall charge of the atom

Nucleus

• Contains positive protons (p+) and neutral neutrons (n0)

• VERY dense

• Occupies only a very small fraction of the atom’s volume

• Makes up more than 99.9% of the atom’s mass

• The electrons (e–) are spread throughout a much larger region (electron cloud) and have a very low mass in comparison with the nucleus (water droplets in a cloud)

protons

• identity of an atom

• number in atoms cannot change

• have similar masses to electrons and are about as 2000 times as heavy as an electron

Protons and neutrons

account for the mass of an atom

electron

is so miniscule comparatively, the mass is negligible

protons and electrons

• There are an equal number of protons and electrons in neutral atoms

  • Protons and electrons account for the charge of an atom

neutrons

contribute no charge

Dalton

• developed his Atomic Theory, he only saw a marble (atom), NOT any particles

  • At this point no one had any concept of anything inside the atom; it was just a solid

J.J Thomson

• used his cathode ray tube to discover these negatively charged particles in the atom and determines their charge-to-mass ratio; the term electron is coined

Robert Milikan

• used his oil-drop apparatus to establishes the charge of the electron

mass of an electron

The charge-to-mass ratio and charge are used to calculate the _

Ernest Rutherford

• accidentally disproved the plum-pudding model using his gold foil experiment, but this leads to the development of the “nuclear atom” and the discovery of protons in the nucleus

James Chadwick

• discovered the neutron

number of protons in its nucleus

What is the most important number to the identity of an atom?

defines the element

number of protons _

Z

The number of protons in an atom’s nucleus is its atomic number and is represented by the symbol

atomic number

number of protons in the nucleus of an atom

chemical symbol

unique one or two letter abbreviation for the elements

Alkali metals

Lithium (Li), sodium (Na), potassium (K), rubidium (Rb),

cesium (Cs), and francium (Fr) are elements groupes in?

Alkali metals

• Shiny, soft, and highly reactive at room temp

• They must be stored in oils to prevent unwanted reaction with air

• Only found naturally in salts

Alkaline earth metals

Beryllium (Be), magnesium (Mg), calcium (Ca), strontium

(Sr), barium (Ba), and radium (Ra) are elements grouped in?

Alkaline earth metals

• Shiny, silvery-white, and somewhat reactive

• All occur naturally

Halogens

Fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and

astatine (At) are elements grouped in?

• Contains elements in all three states of matter

• Form acids when bonded to hydrogen

• Typically produced from minerals or salts

• Cl, Br, and I are often used as disinfectants

Helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon

(Xe), and the radioactive radon (Rn) are elements grouped in?

Noble gases

• All naturally occurring gases

• Typically, highly unreactive

  • Except under extreme conditions

• Metals lie on the left side and the middle of the periodic table

  • Common properties:

    • They are good conductors of heat and electricity

    • They can be pounded into flat sheets (malleability)

    • They can be drawn into wires (ductility)

    • They are often shiny

    • They tend to lose electrons when they undergo chemical changes

Nonmetals

• 17 nonmetals

• Lack properties characterized by metals

• More varied properties

  • Five are solid at room temp. (C, P, S, Se, and I)

  • Eleven are gases at room temp. (H, He, N, O, F, Ne, Cl, Ar , Kr, Xe, and Rn)

  • Bromine (Br) is a liquid

• Poor conductors of heat and electricity

• Carbon is not a metal !

• Not ductile or malleable

• Tend to gain electrons when they undergo chemical changes

metalloids

• The zigzag line between the metals and nonmetals

• AKA: semimetals or semiconductors

  • Intermediate electrical conductivity that can be controlled

• Display a variety of properties

  • Mixture of metallic and nonmetallic

neutrons issues

• All atoms of a given element have the same number of protons

• BUT, they don’t all have the same number of neutrons

• Because the number of neutrons in an atom can vary, not all atoms of the same element have the same mass

  • Neon contains 10 p+, no way around it

  • But neon atoms can contain 10, 11, or 12 neutrons

isotopes

Same number of protons, but different neutrons

percent natural abundance

The relative amount of each naturally occurring isotope is the

same for any given element

mass number (A)

protons + neutrons

A

number of protons + number of neutrons

atomic mass

This is the weighted average mass of all of the naturally occurring isotopes of that element