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.

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

Complete the reading guide worksheet

Due:

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 Characteristics that distinguish elements

from other things Ex. Color, density, odor… Can be observed without altering chemical

structure

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 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

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

Physical Chemical

Copper metal

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 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

2.A.2: Physical and Chemical Properties

Objectives Distinguish between physical and chemical

changes and classify examples of each.

Problem 1: p.111

Consider the statement: Copper compounds are often blue in color. Does this statement describe a physical or chemical property? Why?

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

Answer

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

Burning or combustion of wood- involves a chemical reaction

Wood and oxygen (reactants) change into ash, carbon dioxide and water vapor.

Do Now List at least one chemical property and one

physical property

Homework

Page 112: Questions #1-9

Due: January 16th

Unit 2. A1 Quiz – complete A.1 supplement

worksheet

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

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). Zinc was too reactive for exterior.

C. In 1943, during WWII, Zinc plated steel pennies (quickly corroded)

A.3: Properties of Matter: Designing the Penny 2. Solution

Post 1982 pennies – 97.5% Zinc Copper coating a Zinc core Copper retains the look

of a traditional penny on the

outside and resists corrosion.

Do Now

List at least one chemical property and one physical property

A.4: Chemical Elements

The Periodic Table

Objectives

Identify properties of metals, nonmetals, or metalloids Use this knowledge to complete the lab.

A.4: Chemical Elements Elements are classified in three major

groups: Metals Nonmetals Metalloids

Use the periodic table to distinguish the classes of elements

Periodic Trends

Metal or Nonmetal

Classify each of these elements as a Metal or nonmetal:

Sodium (Na) Aluminum (Al)Calcium (Ca) Carbon (C)Iodine (I) Lead (Pb)Oxygen (O) Nitrogen (N)

Do Now

Identify the three major groups of the periodic table.

Answer

Elements are classified in three major groups: Metals Nonmetals Metalloids

Use the periodic table to distinguish the classes of elements

Periodic Trends

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

Dull in appearance Brittle Do not conduct electricity Ex. Carbon (C), Oxygen (O)

and Sulfur (S)

Solids, liquids or gases

Metalloids Properties of metals and nonmetals

Ex. Silicon (Si) and Germanium (Ge)

Common in the computer

industry

Class Project

A.4 Supplement handout

Due:

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.5: Metal or Nonmetal

Lab

Handout

Periodic Trends

A.6: Periodic Table

1. Review physical and chemical changes 2. Identify trends in the periodic table.

Objectives

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 Table Used to organize elements based on their

similar properties

Dimitri Mendeleev Created a periodic table (1869) of elements

based on:

1. Atomic Weights (written on the periodic table)

2. “Combining Capacity” (how atoms react with other atoms.

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

Turn to page 119 and follow steps #1-6 Try to create your own periodic table based

on several different properties

A.7: Grouping the Elements

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 left-most column are very reactive metals.

All elements in the right-most column are unreactive (noble) gases.

50 years after Mendeleev for explanation.

A.8:

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

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.

Protons

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

The atomic number (number of protons) never changes for an element

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.

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.

Name the 3 subatomic parts of an atom

Question

Answer

Proton – positive charge

Electron – negative charge

Neutron – no charge

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.

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.

Diagram of an Atom

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.

Isotopes

For example, 6 protons + 6 neutrons = mass number of 12 (carbon-12)

6 protons + 7 neutrons = mass number of 13

(carbon-13)

6 protons + 8 neutrons = mass number of 14

(carbon-14)

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.

A.8: Atomic Numbers

Homework: A.8 supplement worksheet

Due: Tuesday, Feb. 11th

A.10: Organization of the Periodic Table

Refer to periodic table

Periodic Trends

Periods: horizontal rows Groups/Families: vertical columns

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).

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 Alkali Metal Family:

Group 1 Highly reactive Metals (sodium)

Alkaline Earth Metal Family: Group 2 Highly reactive Metals (beryllium, magnesium)

Trends in Periodic Families

Transition Metal Family: Groups 3 -12 Metals (iron, copper, gold)

Halogen Family: Group 17 Highly reactive (fluorine, chlorine)

Noble Gas Family: Group 18 Unreactive (chemically inert) elements

(argon, helium neon)

Trends in Periodic Families

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.

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).

Answer sample problem 1

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

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)?

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

Answer sample problem 2

Classwork

Page 126 in text book

Questions 1 – 4

Due:

Homework

Unit 2, A.11 supplement handout Questions 11-15

Predicting properties

Due:

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 between protons and electrons determines physical properties such as melting and boiling points.

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.

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.

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).

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

These properties explain the physical and chemical world around us.

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

What chemical properties must a coin have? Resistance to corrosion and reactivity

with other metals

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

Unit 2, Section A supplement handout