Unit 3 - Atoms: The Building Blocks of Matter

What did John Dalton propose about atoms of the same element? and was he correct?

No, only 21 elements are composed of atoms that are exactly alike in their makeup.

• the majority of the elements have some subtle variations in their atoms that compose them, which are called isotopes

What did John Dalton propose in his Atomic Theory about atoms being divided?

He believed that atoms cannot be divided into anything smaller.

• this is incorrect because atoms are actually made up of smaller particlels within themselves called subatomic particles (protons, electrons, and neutrons).

What did John Dalton propose about an atom’s destructibility?

He believed that atoms are indestructible

• this is in fact incorrect because atoms can be destroyed and are the bases for nuclear weapons and energy.

What did John Dalton propose about atoms when they chemically combine with other atoms?

He was correct about the idea that atoms can only combine with other atoms as whole particles, which is seen in chemical formulas.

• ex. H₂0, can never be H_1/2O

Law of Definite Composition

• applies to ALL compounds

• same elements chemically combine

• same atomic ratio each time the compound is formed

Law of Multiple Proportions

Only applies to a few compounds

Stipulations:

1. must have 2 elements that can form a pair of compounds with each other

2. one of the element’s atomic ratio does not CHANGE (stays constant in both compounds) the other elements atomic ratio does change by some small number

DO EXAMPLES

What are atoms?

• atoms are exceedingly small, cannot see a singular atom

• make up matter

Mass of atoms

• cannot use balance, a mass spectrometer is used

• atomic mass units are used

• 1g = avogadros number (amu)

Which subatomic particle was found first, and info about it?

Protons were

Symbol: p⁺

Charge: +

Location: found inside the atom’s nucleus (center of atom)
Purpose: they are responsible for the atom’s Atomic Number
Mass of a proton: = 1.0073amu
Need to know, called “assigned mass” when rounded to 1amu

Atomic Number: #p⁺ = Atomic Number

Information about Electrons

Symbol: e^-

Charge: -1

Location: found outside of the nucleus

Purpose:

• responsible for the atom’s properties and behavior

• responsible for chemical reactions

• responsible for chemical bonding

Mass: 0.0005486amu (more important: assigned mass is 0amu)

• the mass of an electron is considered to be negligible

Information about Neutrons

Symbol: n^o

Charge: are neutral, no charge

Location:

• found inside the nucleus along with the protons

• Neutrons are nucleons, also “live” in the nucleus

Mass: 1.0087 amu (more important: assigned mass = 1amu)

Purpose:

• contribute to the heftiness or massiveness of the atom (Most Massive Subatomic Particle)

• along with protons, are responsible for the atom’s Mass Number

Atomic Mass

• found on Periodic Table of Elements

• has units of amu or u

• atomic mass: is not used in atomic notation

Mass Number

• does not have units

• #p⁺ + #n^o = mass number

• Mass Number has a symbol: “A”

Information about Charges

• single atoms are loaded with charge!

  • (+) protons

  • (-) electrons

single atom

• charge is neutral

  • quantity of p⁺ and e^- must be equal!

• ex. phosphorus (+15 - protons) + (-15 - electrons) = 0

Charges of atoms when they chemically combine

• when atoms chemically combine, they become charged

• charged atoms are called “Ions”

Cations

(+) charged ion

• atom loses some of its electrons

  • means p⁺ > e^-

Anions

(-) charged ion

• atom keeps all of its electrons and gains a few more

  • means p⁺ < e^-

Coulomb’s Law

attraction/repulsion is inversely related to the distance between the particles

• opposite charges attract when (+) & (-), when they are close to one another

• Like charges repel (-) & (-) or (+) & (+), when they are close to one another

Atomic Notation

• the superscript is the mass number (symbol : A)

• the subscript is the atomic number (symbol : Z)

• A = p⁺ + n⁰

• Z = p⁺

• A - Z = n⁰
  

What is a nuclide?

An atom written in atomic notation

• verbalized as “a nuclide of Sodium 23(mass number)”

• written as Na(symbol) - 23 (mass number)

What charges mean in atomic notation

Na - 23⁺¹

• That atomic number(Z) is 11, means that protons are 11 and electrons are 11. The +1 means that the atom has a positive charge, meaning 1 electron was lost.

• If it were -2, then it is a negative charge, with the atom gaining 2 electrons

• only electrons can be gained or lost because the protons are trapped in the nucleus.

What did John Dalton believe about the similarity between all atoms that compose an element for all elements?

He believed that the atoms are all exactly alike in every capacity for the atoms that compose that element.

• This is only true for 21 elements, the 97 other elements display subtle variation in their atomic form.

Isotopes

ex. Carbon has 3 different forms. C-12, C-13, C-14, all have protons of 6, but different neutrons

• the percent abundances is how much of each isotope composes that element

  • 98.0% is C-12, 1.9% is C-13, 0.1% is C-14.

• All 3 forms of carbon exhibit same properties + behavior, same identity

• Only difference, attains to how heavy because of different amount of neutrons

Information about isotopes part 2.

Iso = same or identical

P = protons

• Nuclides with the same or identical number of protons in their nuclei

• several atomic forms or nuclides, meaning different amount of neutrons

Radioactive Elements

some radioactive elements can also be composed of several nuclides(isotopes). They are called Radionuclides or collectively called radioisotopes

Mass numbers used to distinguish what?

The mass numbers of the most stable nuclide were once used on the periodic table to distinguish the radioactive elements from the “normal” elements.

Isobar

Iso - same or identical

bar - pertains to “heaviness” or weight.

• nuclides that share in common the same mass number

• can be different elements that have different atomic mass(A), but different protons.

• these different elements, when you add up the protons and neutrons will equal the same mass number

• ex. U -235, Np-235, P_⁴ - 23

Isotone

Nuclides that share the same quantity of neutrons

• tone has N, meaning same neutrons