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Chemistry 121

Lectures 1 & 2: Science and the Scientific Method; Chemistry as the Study

of Matter; States and Properties of Matter; An Example of a Chemical

Reaction; Chemical Elements and Symbols; Elements and the Periodic Table Sections 1.1-1.6 in McMurry, Ballantine, et. al. 7th edition

HW #1: 1.42, 1.52, 1.54, 1.64, 1.66, 1.70, 1.76, 1.78, 1.80, 1.82, 1.84, 1.86,

1.92, 1.94, 1.98, 1.106, 1.110, 1.116

Learning Objectives:

1. Identify the main components of the scientific method

2. Understand the differences between physical and chemical properties

3. Identify a transformation as a physical or chemical change

4. Define the 3 phases of matter

5. Understand the difference between: pure substances and mixtures;

elements and compounds; heterogeneous and homogeneous mixtures

6. Distinguish ionic from covalent compounds

7. Introduce metric prefixes to describe the size of particles in true

solutions, colloidal dispersions, and course suspensions

8. Define the colloidal mixture that results when a given phase of matter

is mixed into another phase of matter

9. Describe a chemical reaction, using the oxidation of sodium metal by

chlorine gas, to show the meaning of chemical formulas

10. Describe a chemical reaction, using the combustion of natural gas as

an example, to show the meaning of chemical formulas

11. Determine the number of atoms of a given element in a chemical

formula

12. Identify key elements and groups of the periodic table

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1.1: Chemistry: The Central Science

Chemistry as an Empirical Science

As with other scientific disciplines, chemistry relies on careful

observation and the application of the scientific method

The Scientific Method

Fact (observation) Hypothesis Hypothesis Testing

Hypothesis Testing Data Analysis Acceptance or Rejection of Hypothesis

[Repeated] Acceptance of Hypothesis Theory

Rejection of Hypothesis Modify or discard hypothesis

Question: Which component of the scientific method is most important?

Answer:

Hypothesis testing requires measurement. Given the scale of chemistry, the

scientific method is inextricably tied to technology.

Question: When did we learn cells give rise to new cells?

Answer:

Theories may be modified as new information emerges. The accumulation

and generalization of theories gives rise to the laws of [physical] science

Question: Can a scientific law be invalidated?

Answer:

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1.2: The 3 Phases (States) of Matter

1.3: Classification of Matter

Matter: Has mass and takes up space

Chemistry: The fundamental study of matter. By fundamental, we refer to

the modern view of chemistry based on the building blocks found in the

periodic table (from the Greek atomos, meaning “not to cut”. Initially put

forward by Democritus, ca. 460 – 370 BC)

From a practical standpoint, chemists are interested in the properties of

matter. A property is any characteristic that can be used to describe a

substance. They come in 2 flavors, physical and chemical

Chemical properties: The chemical composition of a substance, as well as the

tendency of a given atom or molecule to react under a given set of conditions

and the physical observations accompanying the reaction

Physical properties: everything else – color, melting point, boiling point,

density, hardness, phase under a given set of pressure and temperature

conditions, ability to mix with other substances, etc.

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A transformation is a change in the properties of a substance over time.

Once again, there are physical and chemical transformations

Chemical Transformation: Chemical reactions, where bonding between atoms

within a pure chemical substance changes

Examples:

The chemical transformation of methane and oxygen to carbon dioxide

and water

The chemical transformation of magnesium and oxygen to magnesium oxide

Physical Transformation: Conversion of atoms or molecules from one phase

to another. Also, the generation or purification of mixtures is a physical

change.

Question: Can you think of an example of a physical transformation?

To summarize, a physical change does not alter the chemical composition of a

substance1, while a chemical change does alter the chemical composition of

the pure substances in question

1 Using differences in physical properties to separate mixtures changes the overall chemical

composition of the sample of matter – and thus the properties - of the resulting substances,

but overall each unique chemical entity remains unchanged. Consider using the boiling point

differences of water and sea salt to purify ocean water

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The conversion of water (H2O, liquid) to steam (H2O, gas) at 100 oC is a physical

transformation as is the melting of potassium metal (K) at 63 oC. The

temperature at which H2O boils is a physical property as is the temperature at

which K melts. The observations associated with the mixing of K and H2O are

chemical, and a highly energy evolving (exothermic) reaction occurs

Problem: Label the following as a physical (p) or chemical (c) transformation

1. The falling of leaves ( )

2. The burning of leaves ( )

3. Water falling over a dam ( )

4. Water turning a turbine to generate electricity ( )

5. Electricity heating a burner on a stove ( )

6. The frying of bacon ( )

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Once again, why is the generation or purification of mixtures a physical change?

Answer:

Classification of Matter Flowchart

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1.4: Chemical Elements and Symbols

Elements

An element consists of a collection of identical atoms (excluding isotopic

differences). Thus elements are pure substances.

Note that the Periodic Table is more completely called the Periodic

Table of the Elements

Those substances representative of an element on the periodic table are

considered to be in their elemental form. Notice these can be monatomic,

diatomic, or polyatomic.

Compounds

Compounds are pure substances made up of 2 or more elements in a fixed ratio

As pure substances, compounds cannot be separated into any other

compounds

Compounds can only be changed by chemical reaction

Compounds generally fall into 2 categories – molecules and ionic compounds

o Examples of ionic compounds: NaCl, CaO

Ionic compounds are composed of oppositely charged particles

held together by the attractive force of opposite electrical

charges

o Examples of molecules: H2O, CH4, CO2

Molecules are held together by the sharing of (negatively charged)

electrons between the (positively charged) nuclei of 2 atoms

o Notice the ratio of the elements in H2O2 and H2O. Are they

the same substance?

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Mixtures

A mixture is any combination of 2 or more pure substances. A mixture can

be either homogeneous or heterogeneous

Homogeneous mixtures are uniform throughout

Heterogeneous mixtures contain areas of differing composition

The distinction of homogeneity or heterogeneity we will use is on the

macroscopic or directly visible scale. There are important distinctions on

the molecular scale. For instance, 2 types of solid in liquid mixtures are the

solution and the suspension

A true solution is uniform down to the molecular level and will remain

homogenous while a suspension occurs when a solid dissolves into a

liquid and the resulting mixture is not uniform at the molecular level.

Course suspensions have particles large enough to be influenced by

gravity and as such will not remain homogenous

o The fact that course suspensions can be separated by gravity is

an important point concerning mixtures in general – you must be

able to separate them by some difference in physical properties

o An important part of chemistry involves purification – taking

complex mixtures and identifying individual pure substances.

The pure substances isolated are generally compounds, since

there are relatively few pure substances found in nature in the

elemental state.

o One can also imagine the reverse process, where pure compounds

(or partially purified complex mixtures) are mixed together in

order to obtain a mixture with optimal physical properties. When

you return home, find a few household products and look at the

ingredients list (for example processed foods, shampoo,

medicines, etc.). A good deal of effort goes into making mixtures

that have ideal properties

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The physical properties of mixtures vary based on the size of the particles

being dispersed (the dispersed phase, minor component) into the continuous

or bulk phase (major component).

True solutions are homogenous at the molecular level and have a particle size

up to 2 nm

A true solution may be colored but will be transparent - true solutions

do not scatter light

Colloidal dispersions are homogenous to the eye and have particle sizes in

the range 2 nm – 0.5 m

Colloidal dispersions will scatter light, giving an opaque, turbid appearance

when light is shined into them. They tend to remain homogenous

Coarse dispersions (course suspensions) are often visible to the naked eye

and have particles of size > 0.5 m

Coarse dispersions tends to separate due to gravitational influence

What then are m and nm?

The 1000x Jump:

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The physical properties of mixtures also vary based on the phase of the

particles being dispersed and the phase of matter being dispersed into. For colloidal dispersions, this gives rise to some commonly encountered forms…

Dispersed Continuous

Liquid Solid Gas

Liquid Emulsion Solid Emulsion

(Gel)

Liquid Aerosol

Solid Suspension

(Sol)

Solid Suspension

(Solid Sol)

Solid or Powder

Aerosol

Gas Foam Solid Foam N/A

A couple of examples from the wonderful world of pharmaceutical science:

On the left is propofol (Diprivan®) used to induce and maintain general

anesthesia; sometimes referred to as “Milk of Amnesia”. Propofol is an

emulsion of soya oil/propofol in water for IV injection. On the right is

Albuterol or Salbutamol (Proventil®, Ventolin®) used to block

vasoconstriction in the asthmatic lung. Albuterol is a fine powder, and is

packaged with a compressed gas propellant for direct inhalation

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1.5: Important Chemical Elements, Their Symbols, and a General

Classification of the Periodic Table

Elements we will focus on:

First 36 Elements (1st 4 Periods)

Group 1:

Group 2:

Group 16:

Group 17:

Group 18:

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1.6: Chemical Reactions – An Example of Chemical Change

Sodium reacted with chlorine gas

The combustion of natural gas

Question: How many oxygen atoms are contained in each of the following

compounds?

C6H12O6 Ca3(PO4)2 2Fe(NO3)3