unit 3: atomic structure sections 1-2. warmup all matter is composed of very small particles called...

Unit 3: Atomic Structure

Sections 1-2

warmupAll matter is composed of very small particles called atoms. In middle school science you learned about the atom.1.Draw a picture of a typical atom. Identify and label the location of the nucleus, electrons, neutrons, protons.

Objective Sections 1-2

I can summarize Dalton's theories.

I can describe properties of protons, neutrons and electrons, who discovered them and where they are found in an atom.

Section 1What is an atom? Describe it’s sizeDefinition: The atom is the smallest particle of

an element that retains the characteristics of that element.

A typical atom is 0.000000001 meters across -- that's one billionth of a meter

Video: Just how small is an atom 5:20

What is an atom?

A. An atom is the smallest particle that can exist

B. An atom is the smallest particle that still has characteristics of an element

C. An atom is a solid sphere, like a marble only really really small

Section 1Dalton’s 4 Postulates (1808)

1.All elements are composed of tiny indivisible particles called atoms

2.Atoms of the same element are identical. Atoms of different elements are different from another element.

3.Atoms of different elements can chemically combine to form compounds

4.Any chemical reaction is simply a re-arrangement of atoms, but the atoms are not changed into different elements.

John Dalton 1776-1844“Father of Modern Chemistry”

Section 2Structure of the atom

Electrons Discovered by

J.J. Thomson in 1897.

Sir Joseph John Thomson (1856-1940)Nobel Prize for Physics (1906)•Discovered the electron•First to discover evidence for isotopes of stable elements.


Thomson created and used a Cathode Ray Tube to study the existence of electrons.

He passed an electric current through a sealed vacuum. Negatively charged electrons are repelled by the negatively charge cathode, and are attracted to the positively charged anode causing a glowing cathode ray to appear

• Thomson - determined the presence of these electrons in all gases and concluded that electrons were part of all atoms

Section 2The Atomic Nucleus In Thomson’s “Plum Pudding Model”:

Scientists assumed the negative electrons were evenly distributed throughout a positive atom.

Which of Dalton’s four theories did J.J. Thomson disprove in his famous CRT experiment?

A. All elements are composed of tiny indivisible particles called atoms

B. Atoms of the same element are identical. Atoms of different elements are different from another element.

C. Atoms of different elements can chemically combine to form compounds

D. Any chemical reaction is simply a re-arrangement of atoms, but the atoms are not changed into different elements.


Robert Millikan - experimented to find the relative electrical charge of an electron to be –1

Millikan discovered electron mass to be 1/1840 of the mass of a hydrogen proton

Electrons in an atom determine its chemical properties

Robert Millikan 1869-1953Nobel Prize for Physics 1923first measured the electron

charge and mass


Protons Since atoms are electrically neutral,

there must be a particle that neutralizes the negative charge of an electron

Protons were discovered by Eugen Goldstein in 1886 who observed additional rays in a cathode ray tube that traveled in the opposite direction of the cathode ray.

Protons have a electrical charge of +1 and a mass of 1 amu.

The number of protons in an atom determines the type of element

Eugen Goldstein1850-1930

discoverer of the proton

Section 2Structure of the atom Neutrons James Chadwick discovered

the existence of neutrons in 1932 using beryllium, alpha rays and known atomic masses.

Neutrons hold the protons together and thus contribute to the stability of the atomic nucleus.

Neutrons have a mass of 1 and no electric charge.

James Chadwick 1891-1974Nobel Prize for Physics 1935

It has a very small mass, and a negative charge. What is it and where is it located in the atom?

A. A Neutron is located outside the nucleusB. A Proton located in the nucleus C. An Electron is located in the nucleusD. An Electron is located in the electron cloud

outside the nucleus.

Section 2Structure of the atom In 1909 Ernest Rutherford

disproves the plum pudding model by bombarding gold foil with alpha particles(+).

Ernest RutherfordNobel Prize for Chemistry 1908


According to the Thomson’s popular “Plum Pudding” atomic theory of the time, the alpha particles should pass through the foil with only a slight deflection

Instead, Rutherford observed that almost all particles went straight thru, but a few of the particles were deflected at odd angles or sometimes directly backwards!!

This result was completely unexpected.

Gold Atom

Section 2Rutherford’s planetary model

Rutherford uses this information to propose a new atomic theory.

The atom is mostly made up of empty space.

The positive charge of the atom, and most of the mass, is concentrated in a small area

This small, dense area is known as the nucleus, and is surrounded by orbiting electrons.

Section 2Rutherford’s Experiment

http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#

Animations Cathode Ray Tube Alpha Particle Scattering …Rutherford’s experiment

= Alpha Particle2 protons + 2 neutrons

In his famous gold foil experiment, Rutherford shot alpha particles into gold. What result did he prove?

A. Atoms have a large diffuse nucleus, like a pudding.

B. Atoms are made up of mostly empty spaceC. Atoms have a small dense positively

charged nucleusD. The nucleus is actually much smaller and

more dense than anyone knew

Atom Facts

Electron Proton Neutron

Charge -1 +1 0

Mass 1/1840(almost negligible)

1 amu 1 amu

Location in Atom

electron cloud nucleus nucleus

Discoverer J.J. Thomson GoldsteinJames

Chadwick

Functiondetermines chemical

properties

determines an elements identity

holds nucleus together

Objective Sections 1-2

To Summarize Dalton’s atomic theory Describe size of an atom Distinguish among protons, electrons

and neutrons in terms of relative mass, charge, location and function

Who Discovered….. the electron? J.J. Thomson the proton? Eugen Goldstein the neutron? James Chadwick

Distinguishing between atomsAtomic Number

Section 3

Atomic Number

Atom Facts Review

Electron Proton Neutron

Charge -1 +1 0

Mass 1/1840(almost negligible)

1 amu 1 amu

Location in Atom

electron cloud nucleus nucleus

Discoverer J.J. Thomson GoldsteinJames

Chadwick

Functiondetermines chemical

properties

determines an elements identity

holds nucleus together

Objective Section 3I can distinguish atoms of different elements and between isotopes and how to name them

Distinguish1. atomic number, 2. mass number3. atomic mass.

I can calculate atomic mass

Section 3Atomic number

The atomic number of an atom is equal to the number of protons in an atom

It is also equal to the number of electrons in a neutral atom

Why would the number of protons and electrons need to be the same in an atom?

Mass Number

The mass of an atom is concentrated in the nucleus and is made up of protons and neutrons

An atom’s mass number is the total number of protons and neutrons in its nucleus.

i.e. Mass # = protons + neutrons The number of neutrons in an atom can be

determined by a quick calculation: Number of neutrons = mass number –

atomic number

What is the mass number of an atom of Beryllium that has 5 neutrons?

A. 4B. 5C. 8D. 9

Mass # = protons + neutrons

An atom of Titanium has 22 protons and has a mass number of 48. How many neutrons are in this atom?

A. 22B. 25C. 26D. 70

Mass # = protons + neutrons

The composition of an atom is given in the following shorthand:

N15

7Protons = ______

Neutrons = ______

Electrons = ______

What element is this?A. calciumB. chlorineC. carbonD. carbonite C14

6

What is the atomic number?

C146

What is the mass number?

C146

How many neutrons in this atom?

C146

Isotopes

Remember! Neutrons in an atom hold the nucleus together and make it stable.

An isotope of an element is an atom of that element with the normal number of protons, but a different number of neutrons.

Isotopes are chemically alike because they have the same number of protons and electrons, but differ slightly from Dalton’s atomic theory since the number of neutrons may differ.

Isotopes are also named using the element’s name followed by the number of protons + neutrons.

example: Carbon-14

Isotopes

Isotopes of Carbon

ProtonsElectron

sNeutron

sName Name

6 6 7 Carbon-13

6 6 8 Carbon-14

6 6 9 Carbon-15

C136

C146

C156

Isotopes

Some highly unstable isotopes can be useful: Carbon – 14: half life: 5730 years

archaeological carbon dating Iodine – 131: half life: 8.02 days

treatment of thyroid disorders Americium – 241: half life: 431.2 years

smoke detectors

Which of Dalton’s four theories was disproven by the discovery that elements have isotopes with differing neutrons?

A. All elements are composed of tiny indivisible particles called atoms

B. Atoms of the same element are identical. Atoms of different elements are different from another element.

C. Atoms of different elements can chemically combine to form compounds

D. Any chemical reaction is simply a re-arrangement of atoms, but the atoms are not changed into different elements.

How to calculate Atomic Mass

Most elements have more than one stable isotope as you find them in nature.

Definition: Atomic Mass the weighted average of the masses of the isotopes of an element.

Some isotopes occur more often than others so the atomic mass of an element is the average of the isotopes’ mass weighted by the abundance of that isotope.

To calculate an element’s atomic mass, you need to know the number of stable isotopes that exist for that element, the mass of each isotope, and the percent abundance of that isotope.

How to calculate Atomic Mass

Example: in any sample of the element neon that you find, there are three isotopes present.

Most of it, 90.48%, is neon-20 19.992 amu

0.27% is neon-21 20.993 amu

9.25% is neon-22 21.991 amu To calculate the average atomic mass multiply the mass of

each isotope by its %abundance and add them together.Neon-20: 19.992 x .9048 = 18.089Neon-21: 20.993x .0027 = 0.057Neon-22: 21.991x .0925 = 2.034

Atomic mass of neon is 20.180 amu Try it this way on your calculator:

19.992 x .9048 + 20.993 x .0027 + 21.991 x .0925 [enter]

Bromine has two naturally occurring isotopes. Calculate the atomic mass.

3579Br = 78.92 amu (50.69% abundant)

3581Br = 80.92 amu (49.31% abundant)

Round to 2 decimal places, Enter numeric answer

use @ key for the . decimal point

Section 4 the Periodic Table

How it came about?

Location, location, location!!!

Objective Section 4

I can describe the origin of the periodic table

Identify the position of key groups, periods and the metals, nonmetals, in the periodic table

Warm up Questions An atom has an atomic number of 4 and a

mass number of 101. How many protons, electrons and neutrons does

this atom have?2. What element is this atom?3. How would you write the name of this isotope?

An atom of aluminum has a mass number of 27.

1. How many protons, electrons and neutrons does this atom have

2. How would you write the name of this isotope of aluminum?

Section 4 – Development of the periodic tableDmitri Mendeleev

A. Dmitri Mendeleev Mendeleev was the first scientist who tried to

organize the elements into a logical pattern.

In 1869, he first listed elements in columns in order of increasing atomic mass.

That arrangement didn’t show any logical trends, so he arranged columns with elements that have similar properties side by side in a table. (p123)

Using this table, he actually predicted the properties of elements yet to be discovered!!!!

Dmitri Mendeleev (1834-1907)

Section 4 – Development of the periodic tableHenry Moseley

Henry Moseley then arranged the elements according to atomic number, keeping the conditions Mendeleev started with.

Moseley’s arrangement allows

us to predict the physical and chemical properties of elements simply based on their location in the table. Henry Moseley

1887-1915

B. The Modern Periodic Table-- The Periods--

Mendeleev’s and Mosley’s discoveries give rise to Periodic Law

Horizontal rows are called periods. There are a total of 7 periods. Periodic law: when the elements are

arranged in order of atomic number, there is a repetition of physical and chemical

properties.Periods go across …..

Periods go across …..

B. The Modern Periodic Table--- the groups -----

Vertical columns are called groups.

The elements in any group tend to have the same physical and chemicals properties.

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There are three general classes of elements:

1. Metals solid at room temp., conduct electricity, ductile, malleable

2. Nonmetals usually non-lustrous, poor conductors of electricity, gases

3. Metalloids intermediate properties between metals and nonmetals

Stair Case divides metals from non-metals

Metals Non-Metals

Metalloids

Significant groups

Alkali metals

Alkaline earth metals

Transition Metals

Halogens

Nobel Gases

Group 1A: Alkali metals = H, Li, Na, K, Rb, Cs, Fr

react violently with waterreact violently with water

Group 2A: Alkaline earth metals = Be, Mg, Ca, Sr, Ba, RaLustrous, Silvery, somewhat reactive

Transition Metals (Group B) all have similar metal properties:solid at room temp., conduct electricity, ductile, malleable

Group 7A: Halogens = F, Cl, Br, I, At

are all nonmetals and are are all nonmetals and are very reactivevery reactive

Group 0 also called Group 8A Noble gases = He, Ne, Ar, Kr, Xe, Rn

are all nonmetals and also known as inert gases because they have virtually no chemical reactivity.

Match the element to its group

Groups Match the property to its group

1. ____ Cesium A. halogen 6. ___ no reactivity

2. ____ Fe B. noble gas 7. ___ silvery, somewhat reactive

3. ____ Sr C. alkali metal 8. ___ all have similar metal properties

4. ____ Neon D. transition metal 9. ___ very reactive non-metals

5.___ Br E. alkaline earth metal 10. ___ react violently with water

Quiz yourself!

Match the element to its group

Groups Match the property to its group

1. _C__ Cesium A. halogen 6. _B_ no reactivity

2. _D__ Fe B. noble gas 7. _E_ silvery, somewhat reactive

3. _E__ Sr C. alkali metal 8. _D_ all have similar metal properties

4. _B__ Neon D. transition metal 9. _A_ very reactive non-metals

5._A_ Br E. alkaline earth metal 10. _C_ react violently with water

Quiz yourself! answers!

unit 3: atomic structure sections 1-2. warmup all matter is composed of very small particles called...

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