Introduction to Chemistry Notes: Atomic Structure Notes

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Introduction to Chemistry Notes
Make sure you can understand these basic questions and concepts so that you can build on the basics to understand the complex material
These are just the basics of what is covered in class lectures. This should not be the only resources you use to study. Who developed the concept of atoms?
What are atoms?
What is the Law of conservation of mass?

What is the law of definite proportions?
What is Dalton’s
Atomic Theory?

Atomic Structure (Experimental Evidence for
Atomic Structure): CH.2
[Section 1]
1.

Circa 400-5 BCE (Greek Philosopher Democritus)
a. Proposed the idea of matter being comprised of small, indivisible, indistructible particles (atomos)
2. Lavoisier (18th century)
a. proposed the law of conservation of mass
i.
matter cannot be created or destroyed ii. atoms cannot be created or destroyed in a chemical reaction, they are simply rearranged to form new substances
3. Proust
a. proposes the law of definite proportions/Law of constant proportions
i.
given compound will always contain the same proportion of chemical elements by mass.
4. Englishman John Dalton (19th Century)
a. formulated the Atomic Theory (aka: Dalton’s Atomic
Theory)
i. concludes the following
1. Matter is composed of tiny particles callled atoms
2. All atoms of a given element are identical 3. The atoms of a given element are different from those of any other given element
4. Atoms of different elements combine in small, whole number ratios to form compounds. A given compound always has the same relative numbers and types of atoms (Law of Definite
Proportions), but different compounds containing the same elements can be formed, by combining elements in different small

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What is the Law of
Multiple proportions?

What is Chemistry?
What are the branches of Chemistry?
Who discovered the
Proton, Neutron, and electron?What are their symbols.

whole number ratios (Law of Multiple proportions) EX.1) 12 grams of carbon can combine with 16 grams of oxygen to form carbon monoxide(CO), but 12 grams of carbon can lso combine with 32 grams of oxygen to form carbon dioxide (CO2). The ratio of oxygen masses that combine with 12 grams of carbon is 16 : 32 or 1
: 2 (whole number ratios)
Experimental Evidence for the Atomic Model:
1. Several experiments were being carried out, and ideas formulated, in the late 19th and 20th centuries that began to identify the subatomic particles that comprise the atom along with their position and nature.

Who came up with the
Periodic Table of
Elements?
How many elements does it contain?

Summary of Early Experiments Used to Formulate Atomic
Theory
Scientist

How is the PTE organized? Experiment
Cathode Ray tube Negative particles of some kind exist Electron

J.J Thomson
(circa 1900)

Cathode Ray deflection Mass: charge ratio of the electron determined

Electron

Milikan
(1908)

Oil drop experiment Charge on the electron Electron

Rutherford,
Marsden, and
Geiger (1909)

Gold foil experiment Nucleus with positive charge present in atom The nucleus of an atom and the proton

Chadwick

Possible existence of

Particles with no charge

Neutron

What is the symobl for reaction? What is the symbol for a gas, liquid, and solid?

What is the yield symbol? Why do we need to balance equations?

Relating

Crookes (Late
19th Century)

What are groups?

What are periods?

Knowledge
Gained

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neutron

exist in atom’s nucleus In the very early 1900’s, the plum-pudding model (electrons dispersed in a “pudding” of positive charge) was the working model.
Modern View of the Atom
1. Niels Bohr
a. took some of Rutherford’s ideas and proposed the idea that the atom was comprised of a dense nucleus containing protons and neutrons that was being orbited by the electron in specific, allowed orbits.
i.
Solar System Model / Plum Pudding Model
(used interexchangably)
2. The atom was thought of as:
What is the Solar
System/Plum Pudding
Model?

What was the atom thought of as?

The atom was thought of as a dense, central nucleus containing protons with a charge of
+1, and a mass of 1 amu
(atomic mass units) and neutrons with a charge of 0 and a mass of 1 amu What was the electron thought of as?

electrons were thought to have a charge of - 1 and a mass of approximately 1/2000 amu that are widely dispersed in specific positions outside of the nucleus. Who introduced wave functions and quantum mechanics? Schrodinger, deBroglie, and Heisenberg introduced wave functions and quantum mechanics to account for the fact that electrons exhibit

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properties that are associated with waves as well as being particles. [SECTION 2]

What is the Periodic
Table of Elements?

What are neutrons?
What are protons?

MAIN IDEA : Each element has a one- or two letter symbol on the periodic table. and two numbers associated with it (Ex. Carbon can be depicted as 6C12 ).
1. The smaller number is called the atomic number
2. The larger number is called the mass number
a. Atomic number (Z) = the number of protons ( positive particles) in the nucleus of one atom of that element i. because all atoms are neutral (carry no electrical charge) it also tells us the number of electrons (negative particles) in the atom. ii. therefore the atomic number of an atom depicts the number of protons and electrons that element contains.
b. Mass number (A) = number of protons + number of neutrons (neutral particles)
c. Isotopes
i.
and elements change in neutrons, different versions of an element

What are electrons?
What is atomic mass?
What is a mass number? What is an atomic number? Why are many mass numbers recorded as non-integer values if the number of protons and neutrons in atoms are always whole numbers?

The reported atomic mass is the average mass of all of the naturally occuring isotopes of an element, and so the mass number can be a non-integer value. Atoms of the same element are defined by the number of protons that they contain; for example, atoms of carbon always have 6 protons and atoms of oxygen always 8, and so on

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Why are many mass numbers recorded as non-integer values if the number of protons and neutrons in atoms are always whole numbers? The number of neutrons present can vary and hence the mass numbers of the same element can vary, too.
Atoms of the same element with different numbers of neutrons are called isotopes.

What are isotopes?

Example Question:
Chromium has four naturally occuring isotopes- 50, 52, 53, and 54 in abundances of 4.350%, 83.79%, 9.500%, and 2.360%, repspectively. What is the average atomic mass of chromium?
a. 48.06
b. 50.06
c. 52.06
d. 54.06
e. 55.06
Calculation :
(Steps)
a. Divide all the abundances by 100.
b. multiply by its respective isotope.
c. add.
(50 x 0.04350) + (52 x 0.8379) + (53 x 0.09500) + (54 x 0.02360) =
52.06
[Section 3]

What are ions?
What are Cations?
What are anions?

MAIN IDEA : Atoms become ions when they cease to be neutral and become charged by either losing or gaining electrons.
1. Electrons are either removed from, or added to, the valence shell of that atom, i.e., the shell that is furthest from the nucleus. 2. Cations - are positive and are formed by losing electrons
3. Anions - are negative and are formed by gainging electrons

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