chem

Lab #3
Atomic Structure & Classification of Matter

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Objectives
Write the correct symbols or names of some elements.
Describe some physical properties of the elements you observe.
Categorize an element as a metal or nonmetal from its physical properties.
Given the complete symbol of an atom, determine its mass number, and the number of protons, neutrons, and electrons.
To identify and classify different types of matter.
Background

Primary substances, called elements, build all the materials about you. Some look similar, but others look unlike anything else. In this experiment, you will describe the physical properties of elements in a laboratory display and determine the location of elements on a blank periodic table. You will also examine different types of matter and classify them according to your observations and knowledge.
A
Physical Properties of Elements
Metals are elements that are usually shiny or have a metallic luster. They are usually good conductors of heat and electricity, ductile (can be drawn into a wire), and malleable (can be molded into a shape). Some metals such as sodium or calcium may have a white coating of oxide formed by reacting with oxygen in the air. If there are cut, you can see the fresh shiny metal underneath. In contrast, nonmetals are not good conductors of heat and electricity, are brittle (not ductile), and appear dull, not shiny.
B
Periodic Table
The periodic table, shown on the inside front cover of your textbook, contains information about each of the elements. On the table, the horizontal rows are periods, and the vertical columns are called groups. Each group contains elements that have similar physical and chemical properties. The groups are numbered across the top of the chart. Elements in Group 1 are the alkali metals, elements in Group 2 are the alkaline earths, and Group 7 contains the halogens. Group 8 contains the noble gases, which are elements that are not very reactive compared to other elements. A dark zigzag line that looks like a staircase separates the metals on the left side from the nonmetals on the right side.
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C
Subatomic Particles
There are different kinds of atoms for each of the elements. Atoms are made up of smaller bits of matter called sub-atomic particles. Protons are positively charged particles, electrons are negatively charged, and neutrons are neutral (no charge). In an atom, the protons and neutrons are tightly packed in the tiny center called the nucleus. Most of the atom is empty space, which contains fast-moving electrons. Electrons are so small that their mass is considered to be negligible compared to the mas of the proton or neutron. The atomic number is equal to the number of protons. The mass number of an atom is the number of protons and neutrons. atomic number = number of protons (p+) mass number = sum of the number of protons and neutrons (p+ + n0)

D
Isotopes
Isotopes are atoms of the same element that differ in the number of neutrons. This means that isotopes of an element have the same number of protons, but different mass numbers. The following example represents the symbol of a sulphur isotope that has 16 protons and 18 neutrons. Complete Symbol of an Isotope mass number (p+ + n0) →
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S

symbol of element →
+

atomic number (p )→

Meaning
This atom has 16 protons and 18 neutrons

16

The element is sulphur
The atom has 16 protons

E
Pure Substances & Mixtures
Matter can be classified by its composition (what it’s composed of) or by its phase (solid, liquid, or gas). We will examine each of these in turn.
Pure Substances
A pure substance may be either an element or a compound. An element is a substance that cannot be decomposed into simpler substances. The graphite in pencils is an example of an element – carbon. No amount of chemical transformation can decompose graphite into simpler substances; it is pure carbon. Other examples of elements include oxygen, a component of air; helium, the gas in helium balloons; and copper, used in plumbing and as a coating on pennies.
The smallest identifiable unit of an element is an atom. There are about 90 different elements in nature and therefore about 90 different kinds of atoms.
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A compound is a substance composed of two or more elements in fixed, definite proportions. Compounds are more common in nature than elements because most elements tend to combine with other elements to form compounds. Water, table salt, and sugar are examples of compounds; they can all be decomposed into simpler substances. The smallest identifiable unit of many compounds is a molecule, two or more atoms bonded together.
Mixtures
A mixture is a combination of two or more pure substances in variable proportions. The pure substances may themselves be either elements or compounds. The flame from a burning log is a good example of a mixture. It contains various gases whose proportions vary considerably from one flame to another. A cup of coffee, a can of soda, and ordinary soil are also examples of mixtures. In fact, most of the matter we encounter is in the form of mixtures.
The air we breathe is a mixture; seawater is a mixture; food is a mixture; we can even think of ourselves as a very complex mixture.
Mixtures may be composed of two or more elements, two or more compounds, or a combination of both. Mixtures can be classified according to how uniformly the substances that compose them mix. A heterogeneous mixture, such as soil and water, is separated into two or more regions with different compositions. A homogeneous mixture, such as salt water, has the same composition throughout.
Solutions (figure 3.1) are homogenous mixtures. Each drop of a true solution is just like every other drop. The individual particles in a mixture are completely integrated with every other particle as you see in figure I. A solution will act like a single substance under most physical tests. How is a solution difference from a pure substance? Recall that a pure substance has one single set of physical and chemical properties. Since a solution can be made up with different proportions of solute and solvent, each different combination will result in different physical measurements.
A colloid (figure 3.2) appears to be a solution. Each drop of a colloid will almost certainly seem like every other drop. But, if you could see the molecules, you would see that a colloid is not truly homogeneous. Instead, many molecules gather together forming a tiny clump of particles (figure 3.2). Many of the items we use every day are not true solutions, they are colloids. A suspension is easy to recognize. You likely have some suspensions in your home now.
Check the bottle; if it says “shake well before using,” you are probably looking at a suspension.
As the name suggests, in a suspension the solute particles are not truly mixed with the solvent.
Instead the particles are ground to a fine powder and float (they are suspended in) the solvent.

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Fig. 3.1

Fig.3.2
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Experimental Procedures
A
Physical Properties of Elements
Materials: A display of elements
Observe the elements in the laboratory display of elements. In the report sheet, write the symbol and atomic number for each element listed. Describe some physical properties such as color and luster. From your observations, identify each element as a metal (M) or a non-metal
(NM).
B
Periodic Table
Materials: Periodic Table, colored pencils, display of elements
B.1

On the incomplete periodic table provided in the report sheet, write the atomic numbers ad symbols of the elements you observed in part A. Write the group number at the top of each column of the representative (Groups 1-8) elements. Write the period numbers for each of the horizontal rows shown. Using different colors, shade in the columns that contain the alkali metals, alkaline earths, halogens, and noble gases. With another color, shade in the transition elements. Draw a heavy line to separate the metals from the non-metals.

B.2

Without looking at the display of elements, use the periodic table to decide whether the elements listed on the report sheet would be metals or nonmetals; shiny or dull. After you complete your predictions, observe those same elements in the display to see if you predicted correctly.
C
Subatomic Particles

For each of the neutral atoms described in the table, write the atomic number, mass number, and number of protons, neutrons, and electrons.
D
Isotopes
Complete the information for each of the isotopes of calcium: the complete nuclear symbol and the number of protons, neutrons, and electrons.

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E
Pure Substances & Mixtures
Go to each of the lab stations and make observations about the objects that are sitting out.
Make as many detailed observations as you can. You do not have to go in any specific order so don’t all bunch up at one station and keep your conversations constructive!
Classify each of the objects as: (some can be more than one!)
 Pure substance
 Compound
 Element
 Homogeneous mixture
 Heterogeneous mixture
 Colloid
 Suspension
Write your observations and classification in the data table provided in the report sheet.

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Report Sheet –Lab 3
Date :
Section:
Instructor:

Name:
Group Members:

Pre-Lab Study Questions
1. Describe the periodic table.

2. Where are the alkali metals and the halogens located on the periodic table?

3. On the following list of elements, circle the symbols of the transition elements and underline the symbols of the halogens:
Mg

Cu

Br

Ag

Ni

Cl

Fe

F

4. Complete the list of names of elements and symbols:
Name of Element
Potassium
Suphur
Nitrogen
Magnesium
Copper

Symbol

Name of Element

Symbol
Na
P
Fe
Cl
Ag

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A. Physical Properties of Elements
Physical Properties
Element

Symbol

Atomic number Color

Luster

Metal/Nonmetal

Aluminum
Carbon
Copper
Iron
Magnesium
Nickel
Phosphorus
Silicon
Silver
Tin
Zinc

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B. Periodic Table
B.1

Questions and Problems
1. From their positions on the periodic table, categorize the following elements as metals (M) or nonmetals (NM).
Na _______ S _________ Cu _______ F _________ Fe ________ C _______
Ca ________
2. Give the name of each of the following elements:
a. Noble gas in Period 2
______________
b. Halogen in Period 2
______________
c. Alkali metal in Period 3
______________
d. Halogen in Period 3
______________
e. Alkali metal in Period 4
______________

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B.2
Element

Metal/Nonmetal

Prediction:
Shiny or Dull

Correct?
Yes/No

Chromium
Gold
Lead
Cadmium
Silicon

C. Subatomic Particles

Element

Atomic number Mass number Protons

Neutrons

Iron

Electrons

30
27

Bromine

80

Gold

197

13
19

20

53

74

D. Isotopes
Nuclear Symbol

Protons

Neutrons

20

Electrons

22

24

20

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Questions and Problems
3. A neutral atom has a mass number of 80 and has 45 neutrons. Write its complete symbol. 4. An atom has two more protons and two more electrons than the atom in question 3.
What is its complete symbol?

E
Pure Substances & Mixtures

Substance

Observation

Classification

Soil
Vinegar
H2O
Chocolate
Chip Cookie
Air
CuCl2
Oil & Water
Aluminum
CoCl2
Starch
CuSO4
Baking Soda

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5. For each of the substances give a detailed reason WHY you assigned each item to its particular classification.
Substance

Rationale for classification

Soil
Vinegar
Water
Cookie
Air
Copper chloride
Oil & water
Aluminum
Cobalt chloride
Starch
Copper Sulfate
Baking Soda

6. Construct a flow-chart (on a separate sheet) that shows the relationship between all of the classifications and how they fit with each other.
7. How is a homogeneous mixture different from a heterogeneous mixture?
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8. How are solutions, colloids, and suspensions different from each other?
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