Download Topic 2 Part 1 Slides - Coral Gables Senior High

Topic 2
Atomic Structure
IB Chemistry SL
Coral Gables Senior High School
Ms. Kiely
Prepare for Lab Quiz:
Put everything away except for a pen (no pencil) and a
calculator.
Bell-Ringer
This is an example of a paper 3 question.
In preparation for an experiment, a student attempts to make a solution that
contains 1 mole of hydrated copper(II) sulfate crystals. He calculates that he will
need [(1 x 63.55) +(1 x 32.07) + (4 x 16.00)] grams of the copper(II) sulfate to
appropriately make the solution. Outline the major error in his calculation.
Atomic Models:
Atomic Models: Democritus
The word atom comes from the Greek word
atomos. Coined by a Greek philosopher named
Democritus in 400 B.C., the word atomos means
indivisible.
Democritus believed all matter was composed of
microscopic, solid, indivisible particles. According
to Democritus’ model, the atom would be a
fundamental particle: the smallest particle of
matter.
Does Democritus’ model of the atom agree with
our current understanding of the atom?
Atomic Models: John Dalton Model
John Dalton was an English chemist who, similar to Democritus, proposed that all
matter was made up of small, indivisible spheres called atoms. Unlike
Democritus, though, Dalton actually had empirical reasoning for this; he
performed many experiments with gases, which led him to his conclusions.
Dalton’s Atomic Theory:
All matter is composed of tiny indivisible particles called atoms
Atoms cannot be created or destroyed
Atoms of different elements are different
Atoms can combine together in small numbers to form
molecules and compounds
● Atoms of the same element are alike in every way
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Was Dalton Right?
True or False: “All matter is composed of tiny indivisible particles called atoms”
False! The atom is NOT fundamental. It is made up of protons, neutrons and
electrons, and therefore is divisible.
Subatomic particles are SO SMALL that instead of describing them by their actual values
we describe their masses by relative values. That is why these values have no units.
Protons and neutrons are relatively the same size, they have a relative mass of 1. Electrons
are about 2,000 times smaller than protons and neutrons, and are therefore given a
relative mass of 0.0005.
Protons are positive with a relative charge of +1; electrons are negative with a relative
charge of -1; neutrons are neutral and therefore have no charge.
Was Dalton Right?
True or False: “Atoms cannot be created or destroyed”
True!
The Law of Conservation of Mass states that mass can neither be created nor
destroyed.
Mass is of course referring to atoms.
Atoms are not destroyed and created
during chemical reactions; they are
only rearranged.
Was Dalton Right?
True or False: “Atoms of different elements are different”
True!
The atomic number, (number of protons in the nucleus), differentiates the atoms
of one element from another.
Was Dalton Right?
True or False: “Atoms can combine together in small numbers to form
molecules and compounds”
True!
Atoms chemically combine together in whole-number ratios to form
compounds and molecules. i.e. H₂O and CO₂
Was Dalton Right?
True or False: “Atoms of the same element are alike in every way”
False!
Even though every atom of one element has the same atomic number, (the same
number of protons in its nucleus), they do not necessarily have to have the same
number of neutrons!
Isotope: isotopes are atoms that have the same number of protons but different
numbers of neutrons.
Each of these nuclei represent
hydrogen because they each only
have 1 proton; however, they are
not alike in every way since they
each have different amounts of
neutrons.
Isotopes are different atoms of the same element with different mass numbers; i.e.
different numbers of neutrons in the nucleus.
Isotopes have the same chemical properties (they react in exactly the same way),
but have different physical properties, such as different melting points, boiling
points, densities, masses, etc.
Isotopes react in the same way because they have the same number of electrons,
and chemical reactions depend only on the number and arrangement of electrons
and not on the composition of the nucleus.
Isotopes have different physical
properties because, for example,
their different masses mean that
their atoms move at different
speeds.
Mass Number of an Atom
We determine the mass of an atom by taking a look at its nucleus.
Mass Number = # of protons + # of neutrons
*
Electrons are SO SMALL that they are not counted when considering the mass of an atom.
Only protons and neutrons determine the mass of an atom.
Example: An atom of Gold (Au) has a mass number of 175. How many protons, neutrons,
and electrons are there in this atom of gold?
P = 79, N= 96, E= 79
AZ Notation & Mass Numbers
A mass number
X chemical symbol
Z atomic number
Test yourself!
1. Information is given about
four different atoms. Which
two atoms are isotopes?
2. State the amount of protons, neutrons, and electrons in the following species:
i) ⁴⁰Ca
ii) ⁵⁰V
iii) ³³P
Relative Atomic Mass (Ar)
Relative Atomic Mass (Ar): the average mass of an element, taking into account all
the mass numbers of all the different types of isotopes that exist for the element
and their respective percent abundances. This value if relative to (one atom of)
12-C. (The definition of RAM would be a 2 mark IB question)
Be careful with the terms mass
number and relative atomic mass!
Mass number refers to the mass of
ONE atom. It is calculated by summing
the protons and neutrons in the
nucleus.
RAM is an average of all the mass
numbers present for an element.
Relative Atomic Mass (RAM)
How do you calculate the RAM of an element?
To calculate the RAM of an element, multiply the mass of each isotope by its
natural abundance (in decimal form), and then add the products.
(Mass # of isotope 1 x Abundance of isotope 1) + (Mass # of isotope 2 x Abundance) + (etc…)
This is done for ALL isotopes that exist for that particular element.
Test Yourself
Consider an element Z that has two naturally occurring isotopes with the
following percent abundances: the isotope with a mass number of 19.0 is
55.0% abundant; the isotope with a mass number of 21.0 is 45.0%
abundant. What is the relative atomic mass for element Z?
You should always calculate RAM values to two places after the decimal.
Test Yourself
The element vanadium has two isotopes,
, and a relative atomic
mass of 50.94. State and explain which isotope is more abundant.