Transcript Atomic Number - Montville.net

Unit 2- Materials:
Structure and Uses
Unit 2- Materials: Structure and Uses
Section 2. A –
Why we use what we do
Do Now
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Read pages. 108-109
Objectives
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1. Define properties and changes.
2. Distinguish between physical and
chemical changes and classify examples of
each.
3. Differentiate between metals, non
metals, and metalloids and their locations
on the period table.
4. Distinguish between isotopes based on
total neutrons.
Unit 2. A.1-A3: Reading Guide
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Complete the reading guide worksheet
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Due:
2.A.1: Properties make the
difference
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What are some materials people of the past
have used as currency?
What makes a material suitable or useable
to produce coins?
How important is appearance or cost?
Answers depend on physical and
chemical properties
Physical Properties
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Characteristics that distinguish elements
from other things
Ex. Color, density, odor…
Can be observed without altering chemical
structure
Physical Properties
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Physical properties and the ability of a
material to undergo physical changes,
such as melting, boiling and bending,
influence the use of that material.
In a physical change, the material
remains the same, although it form
appears to have changed.
Chemical Property
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Describes how the element reacts with
other elements or substances.
When a substance changes into one or
more new substances, it has undergone a
chemical change.
A substance’s chemical properties, often
determine the substance’s usefulness.
Chemical Property
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Chemical change is often observed such
as: formation of a gas or solid, a
permanent color change or a
temperature change.
Physical vs. Chemical Property
Copper
metal
Physical
Chemical
Chemical vs. Physical Changes
Chemical Change
Physical Change
-substance changes
into one or more NEW
substances
-Appearance can change
although chemical structure
remains intact
Example
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Iron RUSTING:
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Observing a chemical change can often mean
the formation of a gas or solid
Thermal energy can be given off or absorbed
Permanent color change
Temperature change
2.A.2: Physical and
Chemical Properties
Objectives
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Distinguish between physical and chemical
changes and classify examples of each.
Problem 1: p.111
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Consider the statement: Copper
compounds are often blue in color. Does
this statement describe a physical or
chemical property? Why?
Answer
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Consider the statement: Copper
compounds are often blue in color. Does
this statement describe a physical or
chemical property?
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Color is a characteristic physical property of
many compounds
Problem 2: p. 111
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Consider this statement: Oxygen gas
supports the burning of wood. Does this
statement refer to the physical or chemical
property of oxygen gas? Explain.
Answer
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Burning or combustion of wood- involves
a chemical reaction
Wood and oxygen (reactants) change into
ash, carbon dioxide and water vapor.
Do Now
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List at least one chemical property and one
physical property
Homework
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Page 112: Questions #1-9
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Due:
Unit 2. A1
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Quiz – complete A.1 supplement
worksheet
A.3: Properties Matter
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Considerations when selecting materials
for a specific use:
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Cost
Desired properties (physical and chemical)
Available in sufficient quantities
A.3: Properties Matter: Designing
the Penny
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1. Cost
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A. Cost of the production of the penny must be
matched by it’s face value ($0.01)
B. Early 1980s Copper became too expensive
and Zinc replaced it in most of the penny
(interior)
C. In 1943, during WWII, Zinc plated steel
pennies (quickly corroded)
A.3: Properties Matter: Designing
the Penny
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2. Solution
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Post 1982 pennies – 97.5% Zinc
Copper coating a Zinc Core
A.4: Chemical Elements
Objectives
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Identify properties of metals, nonmetals, or
metalloids
A.4: Chemical Elements
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Elements are classified in three major
groups:
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Metals
Nonmetals
Metalloids
Use the periodic table to distinguish the
classes of elements
Periodic Trends
Transition Metals
Transition metals
Physical Properties of Metals
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Malleability
Ductility
Luster
Heat conductors and
electrical conductors
Typically reacts with
acids
Ex. Iron (Fe), tin (Sn),
zinc (Zn), and copper
(Cu)
Properties of Nonmetals
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Dull in appearance
Brittle
Do not conduct electricity
Ex. Carbon (C) and Oxygen (O)
Metalloids
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Properties of metals and nonmetals
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Ex. Silicon (Si) and Germanium (Ge)
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Common in the computer
industry
Class Project
A.4 Supplement handout
Due:
Do Now
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List the following as a chemical or physical
change:
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1. A piece of wood burns to form ash.
2. Water evaporates into steam.
3. A piece of cork is cut in half.
4. A bicycle chain rusts.
5. Food is digested in the stomach.
6. Water is absorbed by a paper towel.
7. A change in color
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A.5: Metal or Nonmetal
Lab
Handout
Periodic Trends
A.6: Periodic Table
Objectives
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1. Review physical and chemical changes
2. Identify trends in the periodic table.
Periodic Table
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By the mid-1800’s, chemists has
identified about 60 elements
Five were gases: hydrogen, oxygen,
nitrogen, fluorine and chlorine
Two liquids: bromine and mercury
The rest were solids
A.6: Periodic Table
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Used to organize elements based on their
similar properties
Dimitri Mendeleev
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Created a periodic table (1869) of elements
based on:
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1. Atomic Weights
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2. “Combining Capacity” (how atoms react with
other atoms.
Periodic Table
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Elements with similar chemical
properties were placed in the same
vertical column.
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Horizontal arrangements were based on
increasing atomic weights of the
elements.
A.7: Grouping the Elements
Now you Try
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Turn to page 119 and follow steps #1-6
Try to create your own periodic table based
on several different properties
A.8: The Pattern of Atomic
Numbers
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Creators of early periodic tables were
unable to explain the similarities in
properties among neighboring elements.
All elements in the leftmost column are
very reactive metals.
All elements in the rightmost column are
unreactive (noble) gases.
50 years after Mendeleev for explanation.
A.8:
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All atoms are composed of smaller
particles, including equal numbers of
positively charged protons and negatively
charged electrons.
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Atomic Number – the number of protons
 Identifies each atom as a particular
element.
 Each element has its own unique
atomic number.
 Example: each sodium atom contains
11 protons. Atomic number of sodium
is 11
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The carbon atom contains 6 protons.
Atomic number of sodium is 6
The fluorine atom has 9 protons and
an atomic number of 9
Magnesium has 12 protons and an
atomic number of 12
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Refer to the periodic table to identify
the elements and atomic numbers
(number of protons).
The modern periodic table is arranged
by placing the elements in increasing
atomic number.
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In electrically neutral atoms (no charge)
the number of positively charged protons
equals the number of negatively charged
electrons.
Each sodium atom contains 11 protons
and 11 electrons.
Each carbon atom contains 6 protons and
6 electrons.
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Atomic Weight – the total mass of an
atom.
Atomic weight is equal to the mass of
protons plus the mass of neutrons.
Neutron – an small uncharged particle
found in the nucleus of the atom.
Nucleus – the center of the atom
containing the protons and neutrons.
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Mass Number– equal to the total number
of protons plus the total number of
neutrons.
Generally, the atomic weight of an atom
equals its mass number.
Remember that mass number and atomic
number are not the same.
Isotopes
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While all atoms of a particular element
have the same number of protons, the
number of neutrons can differ from atom
to atom of an element.
Carbon: always has 6 protons, but it
may contain either 6, 7 or 8 neutrons.
Therefore, carbon may have a mass
number of 12, 13 or 14.
Isotopes
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For example, 6 protons + 6 neutrons = mass
number of 12
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6 protons + 7 neutrons = mass number of 13
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6 protons + 8 neutrons = mass number of 14
Isotopes
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Atoms with the same number of protons
but different number of neutrons are
called isotopes.
Isotopes are atoms of the same
element with different mass numbers.
Carbon has 3 isotopes with a mass
number of 12, 13 or 14.
A.8: Atomic Numbers
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Homework: A.8 supplement worksheet
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Due:
A.10: Organization of the Periodic
Table
Refer to periodic table
on page 124
Periodic Trends
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Periods: horizontal rows
Groups/Families: vertical columns
Periods: horizontal rows
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The atomic number (number of protons)
increase from left to right across a row.
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Elements on the left side are chemically
different than elements on the right side
of a row (sodium and chlorine).
Groups/Families: vertical columns
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Each vertical column contains elements
with similar properties (sodium,
potassium and cesium).
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Each vertical column is given a name
based on these similar properties.
Trends in Periodic Families
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Alkali Metal Family:
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Noble Gas Family:
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Group 1
Highly reactive Metals (sodium)
Group 18
Unreactive (chemically inert) elements (argon)
Halogen Family:
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Group 17
Highly reactive (fluorine, chlorine)
A.11: Predicting Properties
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Some element properties can be
estimated by averaging the respective
properties of the elements located just
above and just below an element on the
periodic table.
Mendeleev was able to predict the
properties of many unknown elements
using this method.
Sample problem 1
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Given that the density of silicon (Si) is 2.3
g/cm3 and the density of tin (Sn) is 7.3
g/cm3, estimate the density of germanium
(Ge).
Answer sample problem 1
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Density of silicon (Si) is 2.3 g/cm3 and the
density of tin (Sn) is 7.3 g/cm3
All three elements are in the same group
on the periodic table. Germanium is below
silicon and above tin. Therefore the
predicted density of germanium is 4.8
g/cm3, the average of silicon and tin
densities (actual density is 5.3 g/cm3)
Sample problem 2
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Formulas for chemical compounds can
also be predicted using the periodic table.
For example carbon (C) and oxygen (O)
form carbon dioxide (CO2).
Predict the formula for the combination of
carbon (C) and sulfur (S)?
Answer sample problem 2
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Carbon (C) and oxygen (O) form carbon
dioxide (CO2).
The periodic table indicates sulfur and
oxygen are in the same family (column).
Therefore the predicted formula would be
CS2 – carbon disulfide
Classwork
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Page 126 in text book
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Questions 1 – 4
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Due:
Homework
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Unit 2, A.11 supplement handout
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Predicting properties
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Due:
A.12: What Determines Properties
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Number of protons (atomic number)
determines the identity of the element.
Number and arrangement of electrons
determine many chemical properties.
Interatomic attraction determines physical
properties such as melting and boiling
points.
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A major difference between metals and
nonmetals is that metals lose electrons
while nonmetals gain electrons.
If a metal loses electrons it becomes a
positively charged cation.
If a nonmetal gains electrons it becomes
a negatively charged anion.
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Some physical properties of metals depend
on the attractions among their atoms.
Stronger attractions result in higher melting
and boiling points.
Magnesium has a melting point of 650 oC
and sodium has a melting point of 98 oC.
Attraction of atoms is higher for magnesium
than sodium.
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Chemical and physical properties of
nonmetals also depend on the attractions
among their atoms.
The very high boiling and melting point of
water (Unit 1) is due to the attraction of
the hydrogen and oxygen atoms (positive
and negative attraction).
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Understanding the properties of atoms is
the key to predicting the behavior of
materials.
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These properties explain the physical and
chemical world around us.
A.13: Desired Properties of Coins
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What physical properties must a coin have?
 High melting point and identifiable color
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What physical properties are desirable?
 Size, shape and luster
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What chemical properties must a coin
have?
 Resistance to corrosion and reactivity
with other metals
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What would make the best material for a
new coin: a metal, nonmetal or
metalloid?
 Metals have the appropriate physical
and chemical properties required.
 Nonmetals and metalloids do not.
Homework
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Unit 2, Section A
supplement handout