Chapter 1 Chemical Foundations the structure and behavior of different ... When two elements form a series of compounds, ... The degree of interaction in an atom is determined by

Chapter 1

Chemical Foundations

Chapter 1Table of Contents

Copyright © 2016 Cengage Learning. All Rights Reserved.

(1.1) Chemistry: An atoms-first approach

(1.2) The scientific method

(1.3) The early history of chemistry

(1.4) Fundamental chemical laws

(1.5) Dalton’s atomic theory

(1.6) Early experiments to characterize the atom

(1.7) The modern view of atomic structure: An introduction

Chapter 1


Questions to Consider

How do chemicals in a battery cause the production of electricity?

Why is lead harmful for human consumption?

How do hormones influence human behavior?

How does nail polish remover work?

Section 1.1Chemistry: An Atoms-First Approach


Importance of Studying About Atoms

It provides a better understanding about:

Macroscopic structures and their behavior

Formation of different molecules

Attraction between molecules

Study of chemistry is based on a proper understanding of atoms

Forms the basis of solutions to many problems



Figure 1.1 - Atoms Seen through an STM Microscope



Understanding Atoms

The macroscopic world comprises objects such as cars, glass, rocks, oceans, etc

Made of atoms

Understanding the structure and behavior of different atoms helps in a better purview of the macroscopic world



Figure 1.2 - Grains of Sand on a Beach



Understanding Atoms

There are only about 100 different types of atoms

They combine in various proportions to form all known substances

Properties of a substance are determined by the arrangement of its atoms



Atoms vs. Molecules

Matter is composed of tiny particles called atoms

Atom - The smallest part of an element that is still that element

Molecule - Two or more atoms joined and acting as a unit



Diatomic Molecules

Chemical elements that naturally possess two atoms





A Chemical Reaction

One substance changes to another by reorganizing the way the atoms are attached to each other

Section 1.2The Scientific Method


A sequence that scientists use in the study of nature

Helps solve problems effectively

Mastery of the scientific approach makes for excellent problem solvers

Fundamental Steps of the Scientific Method



Science

A framework for gaining and organizing knowledge

A set of facts with a plan of action

A procedure for processing and understanding certain types of information

Scientific method: The basis on which a scientific enquiry is conducted

It varies according to the nature of the problem encountered



Scientific Models

Theory (model): Set of tested hypotheses that gives an overall explanation of some natural phenomenon

Observation

A witnessed phenomenon that can be recorded

Interpretation

A possible explanation of the reason behind the phenomenon



Scientific Methods

Natural law: An observation that applies to many different systems

Law of conservation of mass: The total mass of materials is not affected by a chemical change in those materials

A law is a statement on how a particular phenomenon occurs

A theory is an attempt to explain why a phenomenon occurs

Section 1.3The Early History of Chemistry


Early History of Chemistry

Greeks were the first to attempt to provide a reason behind chemical equations

They believed that all matter was composed of earth, air, fire, and water

Alchemy was prevalent for the next 2000 years

Several elements were discovered

Methods to prepare mineral acids were developed

Robert Boyle was the first “chemist”

Quantified the relationship between pressure and air

Copyright © Cengage Learning. All rights reserved 17

Section 1.3The Early History of Chemistry


Robert Boyle and Other Pioneers of Chemistry

Introduced quantitative physics and chemistry

Declared that elements cannot be further broken down

Phased out the Greek system of describing elements

All views were not accurate

Metals were not true elements

Georg Stahl

Suggested the existence of phlogiston

Joseph Priestly discovered the existence of oxygen

Section 1.4Fundamental Chemical Laws


Three Important Laws

Law of conservation of mass

Mass is neither created nor destroyed

Stated by Antoine Lavosier

E.g., CH4 + 2O2 CO2 + 2H20

Law of definite proportion

A given compound always contains exactly the same proportion of elements by mass

Stated by Joseph Proust



Three Important Laws

Law of multiple proportions

When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers

Stated by John Dalton



Example 1.1 - Illustrating the Law of Multiple Proportions

The following data were collected for several compounds of nitrogen and oxygen

Show how these data illustrate the law of multiple proportions



Solution

For the law of multiple proportions to hold, the ratios of the masses of nitrogen combining with 1 gram of oxygen in each pair of compounds should be small whole numbers. Therefore, the ratios can be computed as follows

A 1.750 2 = =

B 0.8750 1

B 0.8750 2 = =

C 0.4375 1

A 1.750 4 = =

C 0.4375 1

Section 1.5Dalton’s Atomic Theory


Dalton’s Atomic Theory (1808)

Each element is made up of tiny particles called atoms

The atoms of a given element are identical

The atoms of different elements are different in some fundamental way or ways

Chemical compounds are formed when atoms of different elements combine with each other

A given compound always has the same relative numbers and types of atoms

Copyright © Cengage Learning. All rights reserved 23



Dalton’s Atomic Theory

Chemical reactions involve reorganization of the atoms—changes in the way they are bound together

Atoms themselves are not changed in a chemical reaction



Dalton’s Atomic Theory

Dalton prepared the first table of atomic masses

Also called atomic weights

Most of his masses were not accurate

Incorrect assumptions about the formulas of certain compounds



Concept Check

Which of the following statements regarding Dalton’s atomic theory are still believed to be true?

I. Elements are made of tiny particles called atoms

II. All atoms of a given element are identical

III. A given compound always has the same relative numbers and types of atoms

IV. Atoms are indestructible



Joseph Gay-Lussac and Avogadro (1809–1811)

Joseph Gay-Lussac

Measured the volumes of gases that reacted with each other

Identical conditions of temperature and pressure were used

Avogadro’s hypothesis

At the same temperature and pressure, equal volumes of different gases contain the same number of particles

Applies if the distance between gas particles is very great



Figure 1.8 - Combining Gas Volumes



Figure 1.9 - Combining Gases at the Molecular Level

Section 1.6Early Experiments to Characterize the Atom


J. J. Thomson

Conducted experiments using cathode-ray tubes

High voltage applied to partially evacuated tubes

Assumed that the cathode ray comprised of electrons

Determined the charge-to-mass ratio of an electron

e is the charge of the electron in coulombs

m is the mass in grams

8 = –1.76 × 10 C/ge

m



Figure 1.11 - The Cathode-Ray Tube



The Plum Pudding Model

Hypothesized by Thomson

Atoms are made of a positively charged cloud

Negative electrons are embedded at random



Determining the Charge of an Electron

Robert Millikan

Performed experiments involving charged oil drops

Determined the magnitude of the charge on a single electron

Calculated the mass of the electron

9.11 × 10–31 kg



Figure 1.14 (a) - Determining the Charge of an Electron



Radioactivity

Accidentally discovered by Henri Becquerel

A uranium-containing mineral produced its image on a photographic plate in the dark

Types of radioactive emission

Gamma rays (γ) - High-energy “light”

Beta particles (β) - High-speed electrons

Alpha particles (α) - Possess a charge twice that of the electron, with the opposite sign



The Nuclear Atom

Discovered by Ernest Rutherford in 1911

Alpha particles were made to pass through foil and hit a detector

Some particles were deflected and never hit the detector

Deflection of α particles was attributed to a highly concentrated center of positive charge, which was termed the nucleus



Figure 1.17 (a) and (b) - Expected and Actual Results of the Metal Foil Experiment

Section 1.7The Modern View of Atomic Structure


Composition of an Atom

Protons: Found in the nucleus

Positive charge equal in magnitude to the electron’s negative charge

Electrons: Found outside the nucleus

Negatively charged

Neutrons: Found in the nucleus

No charge

Virtually the same mass as a proton



Composition of an Atom

The nucleus is:

Small compared to the overall size of the atom

Extremely dense

Accounts for almost all of the atom’s mass

A pea-sized nucleus would have a mass of 250 million tons



All Atoms have the Same Components but Different Chemical Properties

Caused by differences in:

The number of electrons

The arrangement of electrons

Electrons of different atoms intermingle to form molecules

The degree of interaction in an atom is determined by the number of electrons it possesses



Isotopes

Atoms with the same number of protons but different numbers of neutrons

11 is the atomic number (Z)

Number of protons

23 is the mass number (A)

Total number of protons and neutrons

2311 Na



Figure 1.19 - Two Isotopes of Sodium



Interactive Example 1.2 - Writing the Symbols for Atoms

Write the symbol for the atom that has an atomic number of 9 and a mass number of 19

How many electrons and how many neutrons does this atom have?



Solution

The atomic number 9 means the atom has 9 protons. This element is called fluorine, symbolized by F. The atom is represented as:

It is called fluorine nineteen. Since the atom has 9 protons, it also must have 9 electrons to achieve electrical neutrality. The mass number gives the total number of protons and neutrons, which means that this atom has 10 neutrons

199 F



Ions

Atoms are electrically neutral

Atoms can be assigned a net charge by either removing or adding an electron

Charged atoms are called ions



Assigning a Charge to an Atom

Atoms are turned into positive ions when they are stripped of an electron

They are called cations

Consider removing an electron from sodium

+ –Na Na + e



Assigning a Charge to Atoms

Atoms are turned into negative ions when an electron is added

They are called anions

Consider adding an electron to chlorine

– – Cl + e Cl

Documents

Chapter 1 Chemical Foundations the structure and behavior of different ... When two elements form a series of compounds, ... The degree of interaction in an atom is determined by