CHEM 1115 & CHEM 1103 Chapter 2: Atoms and the Periodic Table - - PowerPoint PPT Presentation

Chapter 2: Atoms and the Periodic Table

CHEM 1115 & CHEM 1103

Read: Sections 2.1 – 2.9 (all) Textbook Exercises: 2.29, 2.31 a), 2.32, 2.33, 2.42, 2.43, 2.44, 2.45, 2.46, 2.48, 2.49, 2.51, 2.61, 2.62, 2.64, 2.66, 2.68, 2.69, 2.70, 2.72, 2.74, 2.78, 2.80, 2.81, 2.82, 2.86, 2.102 Self –Test (From Study Guide): Multiple Choice (MC) 1, 2, 5, 6, 9, 10, 12 Sentence Completion (SC) 3 - 9, 11 True or False (T/F) 2 - 5, 7 - 9

Atomic Structure: Modern model

Molecular Man

What do atoms look like?

(Image from a scanning tunneling microscope) Carbon monoxide molecules on platinum surface

The Japanese characters for “atom” written with atoms

Nucleus:

• Protons and neutrons (each about equal mass)
• Most of mass
• Very little volume

Outside Nucleus:

• Electrons
• Very little mass
• Most of atom’s volume

Atomic Structure: Modern model

Atomic Structure: An analogy

If this basketball were a hydrogen atom’s nucleus… Average distance to electron would be 2.5 km

Subatomic particle Mass Charge Proton 1.673 x 10-24 g +1 Neutron 1.675 x 10-24 g neutral Electron 9.109 x 10-28 g

• 1

Atomic Structure: Composition

An electron is about 2000 times lighter than a proton or neutron

• The number of protons located in an atom’s nucleus determines

the element’s identity.

• The number of protons in the nucleus of an atom is called the

atomic number.

• Each element has a unique name and symbol.

Symbol has either one or two letters O (oxygen) or Fe (iron)

• The elements are arranged on the periodic table in order of their

atomic numbers

• Elements and names you should know:

https://learn.bcit.ca/d2l/le/content/198204/viewContent/1191199/View

Elements

Atom Notation

X = Atomic symbol Z = Atomic number (also = number of protons in nucleus) A = Mass number (total of protons + neutrons

𝐘

𝐚 𝐁

Isotopes

Isotopes – atoms of the same element with different numbers of neutrons

O

8 16

O

8 18

• xygen-16 oxygen-18

8 protons 10 neutrons 8 protons 8 neutrons

Problem: How many protons, electrons, and neutrons are in the following atoms: protons electrons neutrons

Isotopes and Symbols 𝐓

𝟐𝟕 𝟒𝟑

𝐃𝐯

𝟑𝟘 𝟕𝟔

𝐃

𝟐𝟓

16 16 16 29 29 36 6 6 8

Isotopes and Symbols 𝐓

𝟐𝟕 𝟒𝟑

𝐃𝐯

𝟑𝟘 𝟕𝟔

𝐃

𝟐𝟓

Problem: How many protons, electrons, and neutrons are in the following atoms: ANSWERS protons electrons neutrons

Atomic mass

Mass of an atom in amu (“atomic mass units”) Don’t confuse with mass number (a whole number) Atomic mass of an atom of carbon-12 = exactly 12 amu Each proton and neutron is approximately 1 amu, but not exactly Individual isotopes have different atomic masses; mass in periodic table is weighted average (sometimes called “atomic weight”)

Example: Magnesium has three naturally occurring isotopes with masses of 23.99 amu, 24.99 amu, and 25.98 amu and natural abundances of 78.99%, 10.00%, and 11.01%, respectively. Calculate the atomic weight (average atomic mass) of magnesium. Atomic weight = (% of isotope 1) x (mass of isotope 1) + (average (% of isotope 2) x (mass of isotope 2) + atomic mass) (% of isotope 3) x (mass of isotope 3) + . . .

Electronic structure

An atom of carbon: 6 protons, therefore 6 electrons How are the electrons arranged around the atom? Electrons are in constant motion, and maintain their space around the nucleus at specific energy levels Energy level = n n = 1, 2, 3, 4, …. etc

Electronic structure

Energy level (“Shell”), represented by circles n = 1 up to 2 electrons n = 2 up to 8 electrons Carbon: C

n = 1 n = 2

Shells and subshells (“orbitals”)

Shell Number of subshells Type of subshell 1 1 s 2 2 s, p 3 3 s, p, d 4 4 s, p, d, f

For example: In energy level 1 (shell 1), there is only one type of subshell (s) In energy level 2, there are two types of subshells (s and p), etc. Subshells are also called “orbitals”

Orbitals

Orbitals – regions in space around the nucleus of an atom where electrons are located

Orbital shapes:

s-orbital p-oribitals (px py, pz),

• Electrons arrange in atoms in electron

configurations

• Each orbital can hold up to two electrons
• As orbitals are filled, continue to fill into next

(higher energy) orbitals

• Order of filling orbitals: 1s, 2s, 2p, 3s, 3p, 4s, 3d,

5s, 4p, 6d…. (don’t worry, there is an easy way to remember this)

• “Orbital diagrams” schematically show how

electrons are arranged within each orbital

Electron configurations

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f . . . . 6s 6p 6d 6f . . . .

Electron configurations and orbitals worksheet: https://learn.bcit.ca/d2l/le/content/198204/viewContent/1191005/View

Mg (atomic number 12): 1s2 2s2 2p6 3s2

2 electrons in shell 1 2 electrons in shell 3 8 electrons in shell 2

• The elements are arranged from left to right in increasing atomic number

(number of protons an element has).

• Rows in the periodic table are referred to as periods.
• Columns in the periodic table are sometimes referred to as groups or

families. – Elements within the column have similar physical and chemical properties (because of similar electron configurations)

Periodic Table: Organization

Today’s Periodic Table

= Metal = Metalloid = Nonmetal

Periodic Table: Areas

= Alkali Metals = Alkaline Earth Metals = Noble Gases = Halogens = Transition Metals = Lanthanides = Actinides

Periodic Table: Families