UNIT 2: ATOMIC STRUCTURE C H E M I S T RY 1 - 2 MR. CHUMBLEY

ORIGIN OF THE ATOM CHAPTER 3 SECTION 1 E Q : H O W H A S T H E F U N D A M E N TA L I D E A O F M AT T E R C H A N G E D O V E R TIME?

THE ORIGIN OF THE ATOM • Humans have thought about the existence of matter for a very long time • In ancient Greece, two competing ideas for how matter exists rose to prominence

• The word “atom” comes from the ancient Greek words, “a-” and “-tomos” • This translates to “uncuttables”

DEMOCRITUS’ PARTICLE THEORY OF MATTER • Around 400 BC, a Greek philosopher named Democritus is credited for creating the first model of the atom • While Democritus did not come up with the idea himself, he made it a fuller idea • According to Democritus, “the universe is composed of two elements: the atoms and the void in which they exist and move.”

ARISTOTLE’S CONTINUOUS THEORY OF MATTER • After Democritus’s time, other Greek philosophers came to support a different idea • According to Aristotle, matter was continuous and could be broken down indefinitely • Aristotle’s idea were more widely accepted as the way in which matter existed, and his opinion was accepted for nearly 2000 years

UNDERSTANDING HOW MATTER BEHAVES • By the late 1700’s, most chemists knew and agreed about elements • However, they had difficulty explaining how different substances could combine with one another to form new ones

• This is the origin of modern chemistry, which focused on quantitative analysis of chemical reactions

LAW OF CONSERVATION OF MASS • With the help of improved balances and careful measuring, the first law was discovered • The law of conservation of mass states that matter is neither created nor destroyed during ordinary chemical reactions or physical changes

LAW OF DEFINITE PROPORTIONS • The second discovery was that pure substances have a fixed proportion, regardless of how it is made • The law of definite proportions states that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound

LAW OF MULTIPLE PROPORTIONS • Early chemists also knew that the same elements could combine to create different compounds • The law of multiple proportions states that if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

DALTON’S ATOMIC THEORY • In 1808 John Dalton proposed an explanation that included all three laws • Dalton’s atomic theory has five points: – All matter is composed of extremely small particles called atoms. – Atoms of an element are identical in size, mass and other properties; atoms of different elements differ in size, mass, and other properties. – Atoms cannot be subdivided, created, or destroyed. – Atoms of different elements combine in simple whole-number ratios to form chemical compounds. – In chemical reactions, atoms are combined, separated, or rearranged.

DEMOCRITUS TO DALTON • By using the measurable property of mass, Democritus’s idea was made into Dalton’s scientific theory • While we have since learned that not all points of Dalton’s theory hold true, his basic theory has not been discarded, merely modified and improved

COUNTING ATOMS CHAPTER 3 SECTION 3 E Q : H OW C A N P R OTO N S , N E U T R O N S , A N D E L E C T R O N S B E U S E D TO I D E N T I F Y AT O M S ?

ATOMIC NUMBER • All atoms of an element have the same number of protons • The atomic number of an element is the number of protons of each atom of that element

• Atomic number is noted by the letter Z • In a neutral atom, the number of electrons is equal to the number of protons

ISOTOPES • Atoms of the same element can have different number of neutrons • Isotopes are atoms of the same element that have different masses • Therefore isotopes are atoms with the same number of protons, but different numbers of neutrons • Nuclide is a general term for a specific isotope of an element

MASS NUMBER • Since both protons and neutrons contribute to the mass of the atom, we can find the mass by adding the number of protons to the number of neutrons • The mass number is the total number of protons and neutrons that make up the nucleus of an isotope • Mass number is noted by the letter A

IDENTIFYING ISOTOPES • Isotopes can be identified using hyphen notation that combines the name of the element and the mass number • For example: – uranium-238

– carbon-12 – hydrogen-3

IDENTIFYING ISOTOPES • Isotopes can be identified using the nuclear symbol, which combines the atom’s chemical symbol (X), mass number (A), and atomic number (Z) like so:

𝐴 𝑍𝑋 • For example:

– 238 92𝑈 – 126𝐶

– 31𝐻

SAMPLE PROBLEM A HOW MANY PROTONS, ELECTRONS, AND NEUTRONS ARE THERE IN AN ATOM OF CHLORINE -37?

• Step 1: Analyze – Given: name and mass number of chlorine-37

– Unknown: numbers of protons, electrons, and neutrons

• Step 2: Plan – Atomic number = number of protons = number of electrons – Mass number = number of protons + number of neutrons

SAMPLE PROBLEM A HOW MANY PROTONS, ELECTRONS, AND NEUTRONS ARE THERE IN AN ATOM OF CHLORINE -37?

• Step 3: Solve – The mass number of chlorine-37 is 37. Using the periodic table shows the atomic number of chlorine is 17. Atomic number = number of protons = number of electrons = 17 protons and electrons Number of neutrons = mass number – atomic number = 37 – 17 = 20 neutrons

• An atom of chlorine-37 is made up of 17 electrons, 17 protons, and 20 neutrons

HOMEWORK • Chapter 3, Section 3 – Practice (p.76) #1-3 – Chapter Review (p.86) #8, 11

ATOMIC MASS •

When the mass of a single atom is expressed in kilograms, the value is very small

•

For most calculations it is much easier to use a relative atomic mass

•

One unified atomic mass unit, or 1 u, is exactly 1/12 the mass of a carbon-12 atom

•

Careful calculation of the masses of different isotopes has shown that it differs slightly from the mass number

•

The difference is due to a few factors –

Protons and neutrons deviate slightly from 1 u

–

The mass of electrons is included in the atomic mass

–

A small amount of mass is changed into energy when proton and neutrons combine to form the nucleus

AVERAGE ATOMIC MASS Isotope

Mass #

Abundance

Atomic Mass (u)

• Since most elements occur naturally as isotopes, the mass of that element is determined by the weighted average of those isotopes

Copper-63

63

69.15%

62.929601

Copper-65

65

30.85%

64.927794

• Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element

Average atomic mass calculation:

• The weighting of the mass values is determined by the percentage that isotope has in natural abundance

+

0.6915 × 62.929 601 u 0.3085 × 64.927 794 u 63.55 u

A NEW ATOMIC MODEL CHAPTER 4 SECTION 1 E Q : H OW H A S T H E M O D E L O F T H E AT O M C H A N G E D W I T H T H E D I S C O V E R Y O F S U B AT O M I C PA R T I C L E S ?

MODELS OF THE ATOM • Historically, the model of the atom has changed over time • In the early 20th century, a new model of the atom developed with better understanding of light, waves, and atomic particles • This led to the quantum model of the atom

LIGHT • Light, is a generic term for any kind of electromagnetic radiation • Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space • The electromagnetic spectrum is comprised of all forms of electromagnetic radiation

THE ELECTROMAGNETIC SPECTRUM

BOHR’S MODEL • In 1913, Danish physicist Niels Bohr proposed that electrons can only exist in specific orbits around the nucleus of an atom

• While in a given orbit, an electron neither gains nor loses energy

BOHR’S MODEL • Emission is the process by which an electron falls to a lower energy state, and releases a photon • Absorption is the process by which a photon adds energy to increase the energy state of an electron

EXCITED ELECTRONS GOING TO EXCITED STATE

GOING TO GROUND STATE

EMISSION SPECTRUMS

HYDROGEN SPECTRA

QUANTUM MODEL OF THE ATOM • Additional information has led to a refining of Bohr’s model of the atom • Careful study of the nature of electrons around atoms led to a change in the way atoms are viewed • Quantum theory describes the wave properties of electrons and other very small particles

MODELS OF THE ATOM BOHR’S MODEL (PLANETARY MODEL)

QUANTUM MODEL

HOMEWORK! • Briefly describe what you understand about how the model of the atom changed due to gain of knowledge about light and particles.

HISTORY OF THE PERIODIC TABLE CHAPTER 5 – SECTION 1 E Q : H O W W A S T H E P E R I O D I C TA B L E DEVELOPED?

DEVELOPING THE PERIODIC TABLE • By the mid 1800’s, over 60 elements has been discovered and identified

• Chemists at this time, primarily examined the properties of known elements and compounds containing known elements • In September of 1860, the First International Congress of Chemists was assembled in Karlruhe, Germany to establish standards for determining atomic mass • Italian chemist Stanislao Cannizzaro presented a method to accurately measure relative masses of atoms • This method led to standard values for atomic mass

MENDELEEV’S PERIODIC TABLE • Russian Chemist Dmitri Mendeleev wanted to organize the known elements by their properties

• Mendeleev noticed that when elements were organized by atomic mass, certain properties appeared at regular intervals • These repeating patterns are considered periodic

MENDELEEV’S PERIODIC TABLE • Mendeleev’s table grouped elements with similar properties

• Mendeleev left many gaps in his periodic table, anticipating that there were undiscovered elements

ATOMIC NUMBER • Mendeleev’s Table was very useful, but left two questions unansered: – Why could most elements be arranged in order of increasing atomic mass, but not all?

– What was the reason for chemical periodicity?

• In 1911, English scientist Henry Mosley was examining the emission spectra of many different metals • Mosley noticed that elemental properties aligned better together when they were arranged by atomic number • The periodic law states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements

MODERN PERIODIC TABLES • Modern periodic tables arrange elements by both atomic number and chemical properties • The periodic table is an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same group • The vertical columns of elements the periodic table are called groups or families • The horizontal rows of elements in the periodic table are called periods

NOTABLE GROUPS • Noble Gases – Between 1894 and 1900, all the noble gasses were discovered by a variety of scientists

– These elements had been previously undiscovered since they are totally unreactive

• Lanthanides are the 14 elements with atomic numbers from 58 (cerium) to 71 (lutetium) • Actinides are the 14 elements with atomic numbers from 90 (thorium) to 103 (lawrencium) • Elements in the lanthanides and actinides have very similar properties to each other , but were very difficult to identify and place into the periodic table

MAJOR GROUPS OF THE PERIODIC TA B L E

Alkali Metals Alkaline Earth Metals

Transition Metals Post-Transition Metals Metaloids Non-Metals Halogens Noble Gases Lanthinides

Actinides

MAJOR GROUPS OF THE PERIODIC TABLE •

Alkali Metals –

•

Alkaline Earth Metals –

•

Group 18

Lanthinides –

•

Most of the remaining elements to the right of metalloids

Noble Gases –

•

Specific metals between metals and non-metals moving diagonally from the top of group 13 to the bottom of group 17

Non-Metals –

•

Groups 3-12, with additional metals in groups 13-16

Metaloids –

•

Group 2

Transition Metals –

•

Group 1

Top row of elements removed from period 6

Actinides –

Bottom row of elements removed from period 7

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ELECTRON C O N F I G U R AT I O N S CHAPTER 5 SECTION 2 E Q : H O W D O E S T H E P E R I O D I C TA B L E I N D I C AT E T H E L O C AT I O N O F T H E E L E C T R O N S A R O U N D T H E AT O M ?

ENERGY LEVELS AND ORBITALS • We have previously discussed how electrons exist within specific energy levels around the nucleus of an atom • In addition to energy levels, electrons are located in what are called orbitals

• The orbitals are described as s, p, d, and f • As both the energy level and orbitals increase, so does the complexity of the shape • Valence electrons are found in the outermost shell of an atom and determine its chemical properties

SHAPE OF ORBITALS (P. 103 IN TEXTBOOK)

ELECTRON CONFIGURATION • The arrangement of electrons in an atom is known as the electron configuration • The electron configuration for individual elements helps indicate certain properties • Additionally, elements within the same period have the same electron configuration

ELECTRON CONFIGURATION AND THE PERIODIC TABLE

BELLRINGER! p. 141 Formative Assessment #1-2 1.

To illustrate the relationship between the element’s electron configurations and their placement in the periodic table, into what four blocks can the periodic table be divided?

2.

What is the name given to each of the following groups in the periodic table? a.

Group 1

b.

Group 2

c.

Groups 3-12

d.

Group 17

e.

Group 18