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Chapter 2 Atoms and the Periodic Table

2.1 Atomic Theory & the Structure of Atoms

· The last chapter dealt with chemistry on a large-scale or ______________________ level.

· Now we need to look at matter on a sub-microscopic, or ________________ level.

Questions about the fundamental nature of matter can be traced as far back as theGreek philosophers.

• Aristotle believed that matter could be divided _______________• Democritus argued that there was _________________________

John Dalton proposed atomic theory in 1808.- The smallest particle that an element can be divided into and still be

identifiable is an _______________ , from the Greek atomos, meaning “ _______________."

- All matter is composed of __________- The atoms of a given element differ

from the atoms of all other elements.

Chemical compounds consist of atomscombined in specific ratios.Law of ________________________– atoms combine in whole number ratiosto form compounds.

Water is always H2O, not H2.1O or HO2

Law of ________________________– The same kinds of atoms can combinein more than one proportion. If youchange the ratio, you change thecompound.

H2O is water but H2O2 is hydrogenperoxide

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Chemical reactions change the way that atoms are combined in compounds. Theatoms themselves are unchanged.

2H2 + O2à 2H2OThe Make-up of an AtomAtoms are composed of tiny subatomic particles.The three fundamental subatomic particles are:

• Protons carry a _____________ electrical charge.

• Neutrons have a mass similar to that of a proton,but are electrically __________ .

• Electrons have a mass that is only 1/1836 that of a protonand carry a ________________ electrical charge.

(There are many more particles (e.g., ferions, bosons, etc. that have beenidentified, but these three still provide the core that is needed to understand mostchemical properties and transitions.)Atoms are extremely tiny.

Atomic __________________ range from: Hydrogen at 7.4 x 10-11 m to Cesium at 5.24 x 10-10 mAtomic __________________ range from: Hydrogen at 1.67 x 10-24 g to Uranium at 3.95 x 10-22 gBy comparison, a penny weighs 2.5 g

Characteristics of ParticlesParticle Mass (g) Mass (amu)* ChargeProton (p) 1.672622 x 10-24 1.007276 amu +1Neutron (n) 1.674927 x 10-24 1.008665 amu 0Electron (e-) 9.109328 x 10-28 0.0005486 amu -1

*amu = atomic mass units to be explained laterElectrons are so much lighter that protons and neutrons that their mass is usuallyignored when computing the mass of an atom.

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What is an amu?The masses of subatomic particles are so small that they are hard to work with.

· A scale was devised.· Since carbon is one of the most abundant elements and it is the basis for all

living matter, the relative scale was based on carbon, C.· The basis for the scale is an atom of that contains

protons and neutrons. This carbon atom (known as C-12)is assigned a mass of exactly 12 atomic mass units ( ).

· All other element's masses are defined relative to C-12.

1 amu = 1.660539 x 10-24g (1/12 the mass of one C-12 atom)(an atom with 6 p & 6 n)

Problem: What is the mass, in grams, of a copper atom weighing 62.95 amu?

Problem: How many atoms are in 0.500g of sodium, Na, if each atom of sodiumweights 23.0 amu?

Problem: What is the mass in grams of 2.4x1013 helium atoms, each having amass of 4.0 amu??

How many atoms are in 0.200 g of lithium?a. 6.02 ´ 1023 atomsb. 8.36 ´ 1023 atomsc. 1.74 ´ 1022 atomsd. 2.39 ´ 10−25 atoms

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What is the mass in grams of 2.4 ´ 1013 helium atoms eachhaving a mass of 4.0 amu?a. 1.6 ´ 10−10 gb. 4.0 ´ 10−11 gc. 5.8 ´ 1037 gd. 2.8 ´ 10−37 gArrangement of Subatomic ParticlesThe arrangement of the particles is not random.

- Nucleus- a dense core within the atomthat contains the ___________ and ____________ (and therefore almost allof the mass).

- Surrounding space – is mostly emptyand contains the ______________

- If an atom was the size of a large domedstadium, the nucleus would only occupy avolume the size of a !!!

Structure of the Atom• The structure of the atom is determined

by interplay of different forces.• Opposite electrical charges _____________ each other.• Like charges ____________ each other.

• The positively charged protons attract the negatively charged electrons.- This keeps them in the area around the nucleus.

• Electron repel electrons – So they stay far away from each other.- This accounts for the large space they occupy.

• Protons and neutrons in the nucleus are held together by the ________________________________.

- This takes a lot of energy.

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2.2 Elements and Atomic Number• Atomic Number ( ) is the number of protons in atoms of a given

element.– All atoms of a particular element have the same number of

____________ in the nucleus.

– Since the atom is neutral, they will all have the same number of ____________ .

– They may have different numbers of ____________. - If so they are _____________ of each other.

• Mass Number ( ) is the sum of the protons plus neutrons in an atom.

2.3 Isotopes and Atomic Weight

IsotopesDefinition: Atoms (of the same element) with identical atomic numbers butdifferent mass numbers.

Representation:Mass number ®Atomic number ®Z = atomic number = _______________________.A = _____________________________________

There are three isotopes of hydrogen:

- TortritiumHDordeuteriumHprotiumH 31

21

11

XAZ ¬ Element symbol

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Most isotopes do not have specific names the way those of hydrogen do. Isotopesare usually referred to by their mass number. For example:

U23592 is referred to as _________________________________.

Problem: Which element has atomic number 17?(ANS: Cl)Problem: a)How many protons, neutron, and electrons are in the isotope with

Z=13 and A=27? What is the element?

What is the element?

Problem: How many neutrons are in U-238?

Problem: Complete each of the following isotope symbols:

?115 = Fe56

? =

Atomic Weight

Naturally occurring elements are mixtures of _______________.

Atomic Mass values (aka atomic weights) listed for elements are the weighted ______________ mass of an element’s atoms.

• To calculate the atomic mass, the individual masses of the naturallyoccurring isotopes and the percentage ( as a fractional abundance) of eachmust be known.

Atomic weight = S[(isotope mass) × (isotope abundance)]

The Greek symbol S indicates ________ of terms

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Problem: Copper consists of only two isotopes with masses and abundances of62.95 (70.5%) and 64.96 (??%). Calculate the atomic mass of Cu tothe correct number of significant figures from the data.

2.4 The Periodic Table

History of The Periodic Table• Only elements have been known since the beginning of

recorded history. (Sb, C, Cu, Au, Fe, Pb, Hg, Ag, S, Sn)• By the American Revolution, 24 elements had been identified.• In the late 1700s and early 1800s, as more elements were discovered,

chemists began to look for similarities among elements.• Dmitri Mendeleev organized elements by mass, then into columns based on

________________________ .

Mendeleev’s 1871 Periodic Table• Holes in the table predicted the discovery of new elements.

There are 118 elements currently identified.

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This is the periodic table in the front of your book.

This is the most current one that you can always download. I like the format better.

This is the one we will be using in class. It has the format of webelements.com butthe same atomic weights as your textbook (updated to include new elements).

Most CurrentPeriodic Table fromwebelements.com

Also, excellentinteractive tableon ptable.com

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The names of the most recent 4 elements were only made official in Nov. 2016- Keeping with tradition, the newly discovered elements have been named

after a place or geographical region, or a scientist. The ending of thenames also reflects and maintains historical and chemical consistency:“-ium” for elements 113 and 115 and as for all new elements of groups 1 to16, “-ine” for element 117 and belonging to group 17 and“-on” for element 118 element belonging to group 18.

#113 - Nihonium Nihon is 1 or 2 ways to say

Japan in Japanese.#115 – Moscovium

Discovered in Moscow

#117 – Tennessine Discovered in Tennessee

# 118 – OganessonNamed after scientist Yuri Oganessiana nuclear physics professor at the JointInstitute for Nuclear Research

Using The Periodic TableDemitri Mendeleev arranged his periodic table so that elements with similar propertiesare grouped together.

From 4th ed.

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· Metals (94 of 118): (to the left of the stair-step line)· Semimetals or Metalloids have properties between that of a metal and a

nonmetal.Semimetals / metalloids: Textbooks differ, semimetals are Si, Ge, As, Sb, Te,(Sometimes boron (B), astatine(At) and/or polonium (Po).

We will consider all elements touching the line (except Al) as a semimetal.· Nonmetals: (to the right of the stair-step line)

(Metals to the left of the line, nonmetals to the right)

Each box in the periodic Table gives usspecific information about that element.Based on mass & %abundance of naturallyoccurring isotopes.

Metallic Character

Metal Nonmetal

state

Appearance

Pliability Malleable (bendable)ductile (draws into wire)

Brittle

Conductivity Good conductor Poor conductorDensity

Melting pt.

Reactivity With nonmetals With metals or nonmetals

Examples of Metals –

gold zinc copper

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Examples of Nonmetals –

nitrogen sulfur iodineExamples of semimetals –

boron silicon

- Columns are called ___________________________(elements in the same group exhibit similar chemical behavior)

- _________ Groups - The two groups on the far left ( )and the six on the far right ( ).(These are often designated with an A.)

- ______________________ Groups - Elements in groups ( 3 – 12 ).(These are often designated with an B.)

- _________Transition Metals—The 14 elements following lanthanum are the lanthanides ,and the 14 elements following actinium are the actinides .

- Rows are called Periods

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A graph of atomic radius versus atomic number shows a periodic rise-and-fall pattern. The maxima occur for group elements, and the minimaoccur for group elements.

Problem: Identify the group 5 element in period 4

2.5 Characteristics of Different Groups

Group I (1A) – Alkali Metals- Shiny, ________ metals with low melting points- React with water to form

_____________ solutions.

- Because they are _______________________ ,alkali metals are neverfound in nature in a pure state.

Group 2 (2A) – Alkaline Earth Metals- Lustrous, __________ metals- Reactive, but _______ than their neighbors in group 1Like the alkali metals:- Form alkaline solutions in water.- Never found in nature in the pure state.

An example of aperiodic property