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Unit 2- Materials: Structure and Uses. Unit 2- Materials: Structure and Uses. Section 2. A – Why we use what we do. Do Now. Read pages. 108-109. Objectives. 1. Define properties and changes. 2. Distinguish between physical and chemical changes and classify examples of each.

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unit 2 materials structure and uses
Unit 2- Materials: Structure and Uses

Section 2. A –

Why we use what we do

do now
Do Now
  • Read pages. 108-109
objectives
Objectives
  • 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.
slide5

Unit 2. A.1-A3: Reading Guide

  • Complete the reading guide worksheet
  • Due:
2 a 1 properties make the difference
2.A.1: Properties make the difference
  • 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
Physical Properties
  • Characteristics that distinguish elements from other things
  • Ex. Color, density, odor…
  • Can be observed without altering chemical structure
slide8

Physical Properties

  • 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
Chemical Property
  • 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.
slide10

Chemical Property

  • Chemical change is often observed such as: formation of a gas or solid, a permanent color change or a temperature change.
slide11

Physical vs. Chemical Property

Copper

metal

Physical

Chemical

example
Example
  • Iron RUSTING:
    • 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
slide14

2.A.2: Physical and

Chemical Properties

objectives1
Objectives
  • Distinguish between physical and chemical changes and classify examples of each.
problem 1 p 111
Problem 1: p.111
  • Consider the statement: Copper compounds are often blue in color. Does this statement describe a physical or chemical property? Why?
slide17

Answer

  • Consider the statement: Copper compounds are often blue in color. Does this statement describe a physical or chemical property?
  • Color is a characteristic physical property of many compounds
problem 2 p 111
Problem 2: p. 111
  • 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
Answer
  • Burning or combustion of wood- involves a chemical reaction
  • Wood and oxygen (reactants) change into ash, carbon dioxide and water vapor.
do now1
Do Now
  • List at least one chemical property and one physical property
homework
Homework
  • Page 112: Questions #1-9
  • Due:
unit 2 a1
Unit 2. A1
  • Quiz – complete A.1 supplement

worksheet

slide23

A.3: Properties Matter

  • Considerations when selecting materials
  • for a specific use:
    • Cost
    • Desired properties (physical and chemical)
    • Available in sufficient quantities
a 3 properties matter designing the penny
A.3: Properties Matter: Designing the Penny
  • 1. Cost
    • 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 penny1
A.3: Properties Matter: Designing the Penny
  • 2. Solution
    • Post 1982 pennies – 97.5% Zinc
    • Copper coating a Zinc Core
objectives2
Objectives
  • Identify properties of metals, nonmetals, or metalloids
a 4 chemical elements
A.4: Chemical Elements
  • Elements are classified in three major groups:
    • Metals
    • Nonmetals
    • Metalloids
  • Use the periodic table to distinguish the classes of elements
transition metals
Transition Metals

Transition metals

physical properties of metals
Physical Properties of Metals
  • 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
Properties of Nonmetals
  • Dull in appearance
  • Brittle
  • Do not conduct electricity
  • Ex. Carbon (C) and Oxygen (O)
metalloids
Metalloids
  • Properties of metals and nonmetals
  • Ex. Silicon (Si) and Germanium (Ge)
  • Common in the computer

industry

slide35

Class Project

A.4 Supplement handout

Due:

do now2
Do Now
  • List the following as a chemical or physical change:
  • 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
a 6 periodic table
A.6: Periodic Table
  • 1. Review physical and chemical changes
  • 2. Identify trends in the periodic table.

Objectives

slide42

Periodic Table

  • 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 table1
A.6: Periodic Table
  • Used to organize elements based on their similar properties
dimitri mendeleev
Dimitri Mendeleev
  • Created a periodic table (1869) of elements based on:
    • 1. Atomic Weights
    • 2. “Combining Capacity” (how atoms react with other atoms.
slide45

Periodic Table

  • Elements with similar chemical properties were placed in the same vertical column.
  • Horizontal arrangements were based on increasing atomic weights of the elements.
now you try
Now you Try

A.7: Grouping the Elements

  • Turn to page 119 and follow steps #1-6
  • Try to create your own periodic table based on several different properties
slide47

A.8: The Pattern of Atomic Numbers

  • 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.
slide48

A.8:

  • All atoms are composed of smaller particles, including equal numbers of positively charged protons and negatively charged electrons.
slide49

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
slide50

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
slide51

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.
slide52

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.
slide53

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.
slide54

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.
slide56

Isotopes

  • 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.
slide57

Isotopes

  • For example, 6 protons + 6 neutrons = mass number of 12
  • 6 protons + 7 neutrons = mass number of 13
  • 6 protons + 8 neutrons = mass number of 14
slide58

Isotopes

  • 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.
slide59

A.8: Atomic Numbers

  • Homework: A.8 supplement worksheet
  • Due:
slide60

A.10: Organization of the Periodic Table

Refer to periodic table on page 124

periodic trends2
Periodic Trends
  • Periods: horizontal rows
  • Groups/Families: vertical columns
slide62

Periods: horizontal rows

  • The atomic number (number of protons) increase from left to right across a row.
  • Elements on the left side are chemically different than elements on the right side of a row (sodium and chlorine).
slide63

Groups/Families: vertical columns

  • Each vertical column contains elements with similar properties (sodium, potassium and cesium).
  • Each vertical column is given a name based on these similar properties.
trends in periodic families
Trends in Periodic Families
  • Alkali Metal Family:
    • Group 1
    • Highly reactive Metals (sodium)
  • Noble Gas Family:
    • Group 18
    • Unreactive (chemically inert) elements (argon)
  • Halogen Family:
    • Group 17
    • Highly reactive (fluorine, chlorine)
slide66

A.11: Predicting Properties

  • 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.
slide67

Sample problem 1

  • 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).
slide68

Answer sample problem 1

  • Density of silicon (Si) is 2.3 g/cm3and 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)
slide69

Sample problem 2

  • 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)?
slide70

Answer sample problem 2

  • 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
slide71

Classwork

  • Page 126 in text book
  • Questions 1 – 4
  • Due:
slide72

Homework

  • Unit 2, A.11 supplement handout
  • Predicting properties
  • Due:
slide73

A.12: What Determines Properties

  • 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.
slide74

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.
slide75

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.
slide76

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).
slide77

Understanding the properties of atoms is the key to predicting the behavior of materials.

  • These properties explain the physical and chemical world around us.
slide78

A.13: Desired Properties of Coins

  • What physical properties must a coin have?
    • High melting point and identifiable color
  • What physical properties are desirable?
    • Size, shape and luster
slide79

What chemical properties must a coin have?

    • Resistance to corrosion and reactivity with other metals
slide80

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.
slide81

Homework

  • Unit 2, Section A supplement handout