introduction to atomic structure chemistry chemistry is the study of matter and the changes it...

Introduction to Atomic Structure

Chemistry

Chemistry is the study of matter and the changes it undergoes.

The type of matter that is changing and what types of changes it undergoes determines the field of chemistry that is being studied.

Branches of Chemistry

Physical Chemistry: the study of matter and the physics behind its changes



Biochemistry: the study of the makeup and changes undergone by living species




Analytical Chemistry: The study of the composition (or analysis) of substances





Organic Chemistry: The study of compounds which primarily contain Carbon





Organic Chemistry: The study of compounds which primarily contain Carbon

Inorganic Chemistry: The study of compounds which do NOT contain Carbon

Matter

You will recall that we define matter as anything that has mass and takes up space.

Atoms of an element

Molecules of a diatomic element

Molecules of a compound

Mixture of elements and a compound

Dalton's Postulates

Building on Democritus' idea, in the early 1800s, English chemist John Dalton was the first scientist to observe the physical world and matter and via these observations, this draw some conclusions about atoms.

Dalton's Four Postulates

(1) Matter is made of atoms; atoms are indivisible and indestructible.

(2) All atoms of one element are exactly identical to one another; atoms of different elements are different from one another.

Various atoms and molecules as depicted in John Dalton's 1808 book:

A New System of Chemical Philosophy

Dalton’s Four Postulates

 

(4) Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Hydrogen Oxygen Water

(3) Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

Law of Conservation of Mass

The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place.

click here for an explanation of conservation of mass

26 Which one of the following is not one of the postulates of Dalton's atomic theory?

A Atoms are made of protons, neutrons, and electrons.

B All atoms of a given element are identical

C Atoms are neither created nor destroyed in chemical reactions.

D Compounds are formed when atoms of more than one element combine

E Each element is composed of extremely small particles called atoms.

Scientists

J. J. Thomson (1903)

Discovered electron Electrons have a

negative charge!!Theorized about

protons

Made a piece of equipment called a cathode ray tube.It is a vacuum tube - all the air

has been pumped out.


Thomson’s Experiment

Voltage source

+-

Vacuum tube

Metal Disks


Voltage source

+-

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a Passing an electric current makes a beam appear to move from the beam appear to move from the negative to the positive endnegative to the positive end


Voltage source

+-

Voltage source


By adding an MAGNETIC field

Voltage source


By adding an electric fieldBy adding an electric field

+

-

Voltage source


By adding an MAGNETIC fieldBy adding an MAGNETIC field

+

-

Voltage source


By adding an electric field he found By adding an electric field he found that the moving pieces were negativethat the moving pieces were negative

+

-


Plum-pudding Modelpositive sphere

(pudding) with negative electrons (plums) dispersed throughout

JJ Thomson’s Idea

He knew that the atom contained + and – charges.

The atom was like “Plum Pudding” a mix of + and - .

Ernest Rutherford (1911)

Gold Foil Experiment

Discovered the nucleus

The protons in the nucleus

Rutherford’s experiment

Used radioactive alpha particles to prove the existence of protons.(He+2)

Alpha particles (He+2) - positively charged pieces- helium atoms minus electrons

Shot them at gold foil which can be made a few atoms thick.

Lead block

Uranium

Gold Foil

Fluorescent Screen

What he expected

Because

He thought the mass was evenly distributed in the atom

What he got

Why did JJ believe electrons have charges?

Ernest Rutherford (1911)

Developed the Planetary Modeldense, positive nucleus surrounded by

negative electrons

James Chadwick (1932)

James Chadwick (1932)

Discovered neutronsneutral particles in the

nucleus of an atom

Atom is mostly empty. Small dense,

positive piece at center.

Alpha particles are deflected by

it if they get close enough.

Mass Number

Mass number is simply the sum total of protons and neutrons in the nucleus of an atom. Recall that electrons have insignificant mass compared to protons and neutrons.

C12

6

Mass numbers are always whole numbersMass numbers are NOT on the Periodic Table Atoms of the same element can have different mass numbers

Figuring out number of neutrons in an element

The number of neutrons for any element can be found by subtracting the element's Atomic Number ("Z") from the element's Mass Number ("A")

A - Z = Number of Neutrons

Some elements can have many different numbers of neutrons. Atoms with the same Z but different A are called Isotopes.

Symbols

Symbols on the periodic table contain the symbol (letter) of the element, the mass number and the atomic number

The letter symbol refers to an atom with a specific number of protons.

# protons

# protons + # neutrons mass number

XMass

Number

AtomicNumber

Remember, when the atom is neutral,the number of protons equals electrons

Atomic Number and Mass Number

Atomic Number Number of protons

Atomic Number also equals number of electrons in a neutral atom

12

6

Mass Number

Atomic Number

CMass Number Number of protons + neutrons

12C6

14C6

1 Find the atomic number.

Na2311

Sodium Atom

2 Find the mass number.

Na2311

Sodium Atom

3 How many protons does this element have?

Na2311

Sodium Atom

4 How many electrons does this element have?

Na2311

Sodium Atom

5 How many neutrons does this element have?

Na2311

Sodium Atom

6 Find the atomic number.

Br8035

Bromine Atom

7 Find the mass number.

Br8035

Bromine Atom

8 How many protons does this element have?

Br8035

Bromine Atom

9 How many electrons does this element have?

Br8035

Bromine Atom

10 How many neutrons does this element have?

Br8035

Bromine Atom

1 The atomic number indicates __________.

A the number of neutrons in a nucleus

B the total number of neutrons and protons in a nucleus

C the number of protons or electrons in a neutral atom

D the number of atoms in 1 g of an element

E I don't know how to answer this question.

introduction to atomic structure chemistry chemistry is the study of matter and the changes it...

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