Introduction to General Chemistry

What is Chemistry?

• Chemistry is the study of properties of substances and how they react

• Chemical substances are composed of matter– Matter is the physical material of the universe; anything

with mass that occupies space (volume) is matter

– Matter can take numerous forms

– Most matter is formed by unique arrangements of elementary substances called elements

Elements, Compounds, and Molecules

• An element can easily be defined as a substance that can not be broken down into simpler substances

• Millions of different materials in the world, all comprised of some combination of only 118 elements

– Similar to how the alphabet combines 26 letters to yield hundreds of thousands of words, elements bond in unique arrangements to give different molecules

– Molecules agglomerate to yield compounds

Elements, Compounds, and Molecules

• An element can easily be defined as a substance that can not be broken down into simpler substances

• Millions of different materials in the world, all comprised of some combination of only 118 elements

– Similar to how the alphabet combines 26 letters to yield hundreds of thousands of words, elements bond in unique arrangements to give different molecules

– Molecules agglomerate to yield compounds

HO O

H

HO

H

Molecules Are Comprised of Uniquely Arranged Atoms. Different Molecules Have Different Properties.

ethanolacetic acid

acetaldehyde (hangover) carbon dioxide

methanol

BLINDNESS!!!

Small Molecular Differences Can Yield Vastly Differentin Terms of Biological Interactions

Relief of Morning Sickness Severe Limb Defects

Small Molecular Differences Can Yield Vastly Differentin Terms of Biological Interactions

C6H12O6 C6H12O6

Technically, glucose and fructose are the same. So is high fructose corn syrup really that bad for you???

Small Molecular Differences Can Yield Vastly Differentin Terms of Biological Interactions

Small Molecular Differences Can Yield Vastly Differentin Terms of Biological Interactions

Na (sodium metal) Cl2 (chlorine gas)

Na+Cl-

The Properties of Molecules Differ Vastly from those of the Atoms That Comprise Them

Different atomic arrangements can change physical properties

Carbon (graphite vs diamond)

Spatial Dimensions of Compounds Can Alter Properties

5 nm 50 nm

Bulk GoldGold Nanoparticles

Spatial Dimensions of Compounds Can Alter Properties

CdSe quantum dots

2 nm 12 nm

Solids• Atoms tightly bound• Fixed volume and shape (does not

conform to container)• A chemical is denoted as solid by

labeling it with (s)

Phases of Matter: Solids, Liquids and Gases

S(s)

Liquids• Atoms less tightly bound than

solids• Has a definite volume, but not

definite shape (assumes the shape of its container)

• Denoted by (L)

Phases of Matter: Solids, Liquids and Gases

H2O (L)

Gases• Free atoms• No shape, no definite volume• Can be expanded or compressed

(like engine piston)• Denoted by (g) ; ex. O2 (g)

Phases of Matter: Solids, Liquids and Gases

What Are Atoms Made Of?

• The mass of an atom is derived from the subatomic particlesthat compose it. These electrically charged particles are known as:– electrons (negatively charged)

• Very small, nearly massless particles• Responsible for chemical reactions and chemical behavior

– protons (positively charged)• Much heavier than electrons.• Number of protons defines the element. No two differing elements

have the same number of protons.• Play no role at all in chemical reactions, but are involved in nuclear

reactions (A process in which one or more elements react to become another, such as fusion or fission)

– neutrons (neutral)• Equal mass to protons• Act as a buffer between protons to minimize repulsive interactions• Also involved in nuclear reactions.

Atomic Structure

• The structure of the atom is a spherical system possessing a centralized, highly dense nucleus composed of tightly packed protons and neutrons, with a surrounding sparse cloud of electrons.

• Virtually all of the atom’s mass is in the nucleus.

• We can express the masses of these tiny particles using the atomic mass unit (amu = 1.66 x 10-24g)

Particle Relative Charge Mass (amu)

Electron -1 .000548

Proton +1 1.007

Neutron 0 1.008

Atomic Symbols

• The number of protons in an atom is called the atomic number. This number defines an element.

• As shown to the right, only Helium can have 2 protons.

• The atoms of a given element are exactly the same in every way.

• Since nearly all of the mass of an element is in the nucleus, and the masses of these particles is ~1 amu, the atomic mass is merely the sum of the number of protons and neutrons

Isotopes

• As you may have noticed, atomic masses are not whole numbers.

• The atomic masses listed on the periodic table are weighted average values.

• The reason for these averages is that numerous variation of elements exist in nature called isotopes.

Isotopes

• Isotopes are variations of a element containing different numbers of neutrons in the nucleus. We can represent these with isotope symbols, as shown to the bottom right for Hydrogen.

• The most common isotope of hydrogen has one proton, no neutrons, and one electron (mass # = 1, 99.985% of all hydrogen atoms).

• There is a 2nd isotope of hydrogen found in nature (deuterium) which has one neutron (mass # = 2, 0.0115 % of all hydrogen atoms)

• Ex. If you had 2000 Hydrogen atoms in a jar, 1997 of them would have 0 neutrons, and 3 of them would have 1. The average mass of the 2000 atoms is the atomic mass on the periodic table.

Calculating Average Atomic Mass

• The average atomic mass of an atom can be calculated by adding together the mass contributions of each isotope, according to the equation below, where the abundance is represented in decimal form:

• Ex. Oxygen has 3 isotopes, as listed in the table below. Calculate the average atomic mass and compare your value to the periodic table.

𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀 𝐀𝐀𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚 𝐚𝐚𝐀𝐀𝐦𝐦𝐦𝐦 = � 𝐀𝐀𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐀𝐀𝐚𝐚𝐚𝐚𝐀𝐀 𝐱𝐱 (𝐚𝐚𝐦𝐦𝐚𝐚𝐚𝐚𝐚𝐚𝐢𝐢𝐚𝐚𝐚𝐚 𝐚𝐚𝐀𝐀𝐦𝐦𝐦𝐦)

Calculating Average Atomic Mass

𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀 𝐀𝐀𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚 𝐚𝐚𝐀𝐀𝐦𝐦𝐦𝐦 = � 𝐀𝐀𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐀𝐀𝐚𝐚𝐚𝐚𝐀𝐀 𝐱𝐱 𝐚𝐚𝐦𝐦𝐚𝐚𝐚𝐚𝐚𝐚𝐢𝐢𝐚𝐚𝐚𝐚 𝐚𝐚𝐀𝐀𝐦𝐦𝐦𝐦

𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀 𝐀𝐀𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚 𝐚𝐚𝐀𝐀𝐦𝐦𝐦𝐦= 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 8

16𝑂𝑂 𝑚𝑚𝑎𝑎𝑚𝑚𝑚𝑚 816𝑂𝑂 + 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 8

17𝑂𝑂 𝑚𝑚𝑎𝑎𝑚𝑚𝑚𝑚 817𝑂𝑂 +

𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 818𝑂𝑂 𝑚𝑚𝑎𝑎𝑚𝑚𝑚𝑚 8

18𝑂𝑂

𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀𝐀 𝐀𝐀𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚𝐚 𝐚𝐚𝐀𝐀𝐦𝐦𝐦𝐦 = 0.9976 15.995 + 0.00038 16.999 +0.00200 17.999 = 𝟏𝟏𝟏𝟏.𝟗𝟗𝟗𝟗𝟗𝟗 𝐀𝐀𝐚𝐚𝐚𝐚

How Did The Elements Form?

1. All of the matter of the universe was compressed into one infinitely dense, infinitely hot mass that expanded with tremendous force. This event is known as the big bang.

2. In an instant, the universe was formed and began to expand exponentially in all directions, causing the matter to cool

3. After several microseconds, energy released from the event was converted into mass, forming the first protons, electrons and neutrons

4. Electrons combined with the protons and neutrons to form the first hydrogen isotopes

5. Giant clouds of hydrogen came together to form stars6. Within the stars, enormous amounts of heat provided hydrogen

atoms with enough kinetic energy that their collisions would result in a nuclear reaction known as fusion.

How Did The Elements Form?

01𝑎𝑎1

3𝐻𝐻

24𝐻𝐻1

2𝐻𝐻

• For most of their lives, stars fuse hydrogen into helium in their cores. These reactions account for 85% of the Sun’s energy. The remaining 15% comes from fusion reactions between hydrogen and helium to produce lithium, or the fusion of two helium atoms to produce beryllium.

• The star is sustained because these fusion reactions release huge amounts of heat which allows the star to expand against gravity

Phases of Matter: Solids, Liquids and Gases

• When a star’s core runs out of hydrogen, the star begins to die out. The dying star expands into a red giant, and this now begins to manufacture carbon atoms by fusing helium atoms.

• More massive stars begin a further series of nuclear burning or reaction stages. The elements formed in these stages range from oxygen through to iron.

Formation of Rare Heavy Elements

• Once a star begins to form Fe, its death is imminent. The fusion of Fe, unlike lighter elements, absorbs energy. Thus, as iron forms, the star cools down.

• Eventually, gravity wins and the star collapses inward. However, the outer gas layer can’t penetrate the iron core, so the implosion reverses course and explodes outward. The energy from this event creates all elements heavier that iron.

• Thus far, we’ve learned than an element is essentially defined by it’s atomic number

• We have also learned that isotopes of a particular element can have variations in the number of neutrons.

• Next, we will discuss ions.

Ions

• Ions are electrically charged atoms, resulting from the gain or loss of electrons, which occurs during the course of a chemical reaction.

• Positively charged ions are created when an atoms loses electrons. These are called cations.

• Negatively charged ions are created when an atom receives electrons. These are called anions.

• Typically, cations are named by adding the word “ion” to the end of the element name. Anions are named by adding the suffix –ide to the end of an element

Ions

𝐿𝐿𝐿𝐿+

𝑁𝑁𝑎𝑎+

𝑀𝑀𝑀𝑀2+

𝐴𝐴𝐴𝐴3+

Lithium ion

Sodium ion

Magnesium ion

Aluminum ion

𝐶𝐶𝐴𝐴−

𝑆𝑆2−

𝑂𝑂2−

𝑃𝑃3−

Chloride

Sulfide

Oxide

Phosphide

Ions

1632𝑆𝑆Sulfur

1632𝑆𝑆2−

Sulfide

ISOTOPE Protons Neutrons Electrons

1632𝑆𝑆

1632𝑆𝑆 2-

1327𝐴𝐴𝐴𝐴 13

27𝐴𝐴𝐴𝐴3+ionized

Aluminum Aluminum ion

ISOTOPE Protons Neutrons Electrons

1327𝐴𝐴𝐴𝐴

1327𝐴𝐴𝐴𝐴 3+

ionized

• Fill in the tables below

Ions