Download Chapter 3: Atoms and Moles

Chapter 3: Atoms and
Moles
Mr. Hua
Warm-Up (09/02/14)
Draw an atom. Label
all parts, if any.
What is a compound?
(hint: related to atoms)
Precision vs. Accuracy
 Scientists need to be precise and
accurate when making measurements
 Precision – the exactness of a
measurement; measures how close
multiple measurements are
 Accuracy – description of how close a
measurement is to the true value
Precision
 You are precise when you are consistent.
 You weigh out something 3 times and get
3.9g, 4.0g, and 4.1g.
 All these numbers are similar and agree
with each other
 The actual value was 4.5 so these ARE
NOT accurate.
Precision vs. Accuracy
Accuracy
How close your measurement is
compared to the true or actual
value
I ask you to weigh 5g of a
substance. You weigh 5.3g, 5.7g,
and 4.5g. Which number is the
most accurate?
Significant Figures
 Tells your how many digits to record
 There are many rules
 In a problem, use the same number of
figures given
 Ex. What is 10.5 x 9.45? (Answer is 99.225,
but your answer should be rounded to 99.2)
[3 sig figs]
 Write out all measurements as given by
devices
History of the Atom
 What are the building blocks of all
matter?
 400 BC : Democritus came up
with the idea that there’s a limit
to how much you can divide
something; There is a unit that is
indivisible, the atom (atomic
theory)
Warm-Up (09/03/14)
Atoms can be divided into
three parts. What are
these parts?
What charge (positive,
negative, neutral) do these
parts have?
Please come in
and sit quietly.
Take out 1 sheet
of paper.
POP QUIZ Period 6 Only
1.When two or more atoms of
different elements combine,
they form _____________.
2.Explain the difference between
precision and accuracy. You
may use pictures/diagrams.
History of the Atom
 What are the building blocks of all
matter?
 400 BC : Democritus came up
with the idea that there’s a limit
to how much you can divide
something; There is a unit that is
indivisible, the atom (atomic
theory)
Law of Definite Proportions
A chemical compound
always contains the same
elements in exactly the
same proportions by
weight/mass
Law of Definite Proportions
Ex. Table salt, or NaCl is
always made of sodium and
chloride in the same
proportions
By mass: 60.66% Chlorine
and 39.34% Sodium
Law of conservation of mass
Mass cannot
be created or
destroyed
Dalton’s Atomic Theory
1. Atoms cannot be
subdivided, created or
destroyed
2. All atoms of an element are
identical
Are these true or false?
FALSE!!!!!!!
Dalton’s Atomic Theory
1.
Has been modified
2.
Has been modified
3. Atoms of different elements differ in their
__________ and ___________
properties
4. Atoms of different elements combine in
simple, whole number ratios to form
_____________.
5. In ___________ reactions, atoms
combine, separate, and rearrange, but
are never created, destroyed or
changed.
Cathode Ray Experiment
(J.J. Thomson)
Exit Slip (don’t write ?s)
Why is it important to study the
atom before other chemistry
topics?
How did Thomson determine
electrons were negatively charged?
One question or thing you’d like to
know more about atoms
Warm-Up
th
(September 4 )
I ask you to weigh something
that is known to be 30g. Give
me 3 measurements that are
precise. What are 2 accurate
measurements?
Thomson’s Atom Model
Plum-pudding model:
negative electrons in a ball of
positive charge
Protons + Neutrons = Nucleus
 Nucleus: atom’s central region; contains most
of the atom’s mass
 The nucleus is much smaller than the entire
atom
 Radius of an atom is 10,000x larger
Atomic Number
 Atomic number = number of protons
 Protons and electrons have equal and
opposite charge, so for neutral atoms, #
protons = # electrons
Atomic Number
 Atomic number = number of protons
 Protons and electrons have equal and
opposite charge, so for neutral atoms, #
protons = # electrons
Element name
Atomic symbol
Atomic number
(#protons)
Mass
number
Mass Number
 Mass Number – Atomic Number = Number of Neutrons
Atomic number
(#protons)
Mass
number
Calculate the number of
neutrons in Aluminum
Isotopes
 Isotope: An atom that has the same number of
protons but different number of neutrons than
other atoms of the same element
Mass number
Atomic Number
(#protons)
How many
neutrons?
Class Practice
 How many
protons?
 How many
electrons?
 How many
neutrons?
 Atomic
mass?
Isotopes Practice
 How many protons and neutrons
are in a regular Uranium atom?
What is it’s mass number?
 How many protons and neutrons
are in Uranium-235?
 What is the difference between
them?
Warm-Up (Sep 9,2014)
Draw the model of an atom
and include protons,
neutrons, and electrons.
Why do scientists use
models?
Rutherford’s Atomic Model
 Rutherford proposed electron orbits
 What is wrong with his model?
Bohr’s Atomic Model
Electrons are
confined to
assigned energy
levels
Closer to nucleus
 lowest energy
level
Electrons Act Like Both
Particles and Waves
 Electrons have mass  particle
 Electrons are confined to the space around a
nucleus
 Electrons  waves with specific frequencies (energy levels)
 Electrons are located in orbitals (electron
clouds)
Electrons, energy, and Light
 Normally, electrons will be in the ground
state – the lowest possible energy
 If an electron gains energy, it moves to an
excited state (more energy)
What happened? (Think of
electrons, energy, light)
Energy is emitted as
wavelengths of light
Counting Atoms
 Atomic mass – mass of an
atom expressed in atomic
mass units (AMU) [Same
number as mass number]
 Mole – SI unit used to measure amount of
substance
 Carbon-12 used as the standard for the atomic mass scale
 Molar mass – the mass in grams of 1 mol of
a substance (g/mol)
 Avogadro’s number – 6.022 x1023 ; the
number of atoms/molecules in 1 mol
Practice Problem
What is the mass (in
grams) of 1.0 mol of
aluminum?
What is the mass of
2.0 mol of Al?
How many moles are in 27g of
Aluminum?
Practice Problem #2
 How many moles of
Nitrogen are
represented by 35g
of Nitrogen?
 What is the mass of
4.5 mol of Nitrogen?