Download Lecture 2 - Unit 1 Part 2 Slides

Isotopes and the Mass of
an Atom
Unit 1, Part 2
Ch. 2 & 4
Coral Gables Senior High
Ms. Kiely
Pre-IB Chemistry I
Bell-Ringer #1
How are the atoms of one element different from the atoms of another
element?
Back to Part 1 Slides
Review:
I.
II.
The atom is made up of three subatomic particles: the proton, the neutron, and the
electron.
Protons and neutrons (nucleons) are located in the center of an atom; a region called the
nucleus. Electrons are found very far from the nucleus, surrounding the nucleus in what we
call the electron cloud.
III.
Protons and neutrons are further broken down into quarks. Electrons, however, are
fundamental particles; they cannot be further broken down/are not made up of smaller
particles.
Review:
IV.
The atomic number, number of protons in the nucleus, differentiates the atoms of one
element from the atoms of other elements.
V. The state that matter is in depends on the kinetic energy of its particles
Element: an element is anything that consists
of one type of atom.
*Molecule: the term molecule is often
misused. The term “molecule” is also used to
describe atoms that are bonded together;
however, it is only used when the bonded
atoms are nonmetal atoms! Also, the
nonmetal atoms that are bonded together
can be of the same element or be of different
elements.
Compound: a substance made by
chemically combining two or more
elements. It has different properties
from its constituent elements.
Matter is either pure or mixed.
Pure matter is anything that is made up of only one type of atom (an element), or one type
of compound.
Mixed matter is anything that is made up of different elements and compounds that are not
chemically bonded together.
John Dalton
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
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.
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.
1. Carbon has many isotopes. If you find an isotope of carbon that has a mass
number of 13, how many neutrons does the atom have?
2. Why are O-16, O-17, and O-18 examples of isotopes?
3. How many protons and neutrons do O-16, O-17, and O-18 have,
respectively?
Mass Numbers
Since we know that isotopes exist, we know that not all atoms of an element are
identical. All the atoms of an element will have the same number of protons,
but not necessarily the same number of neutrons.
This means that some atoms of an element have more mass than others!
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 considered when determining the mass of an
atom.
Mass Numbers
Practice:
1) What is the mass of an Oxygen atom that contains 9 neutrons?
2) An atom of Silver (Ag) has a mass number of 115. How many protons,
neutrons, and electrons are there in this atom of Silver?
AZ Notation
A mass number
X chemical symbol
Z atomic number
Another type of notation:
Whenever you see a dash present between a chemical symbol and a number,
you can be assured that number is the mass number of that particular atom.
C-12
C-14
C-13
Proton: ____
Proton: ____
Proton: ____
Neutrons: ____
Neutrons: ____
Neutrons: ____
Electrons: ____
Electrons: ____
Electrons: ____
3
4
3
Matter has mass and occupies volume.
Mass: refers to the amount of matter.
Volume: refers to the amount of space occupied by
matter.
Tennis balls are much larger than golf balls, and
therefore have a larger volume than golf balls do since
they occupy more space.
Tennis balls have less mass than golf balls, though.
Why?
Review
Identify the subatomic particles present in an atom of ²²⁶Ra.
Video: Crash Course Chemistry: The Nucleus