4-1: Introduction to Atoms

How did the atomic theory develop and change into the modern model of the atom?

Anticipatory Set

Here come the atoms!

http://www.miamisci.org/af/sln/

California StandardsScience Standard 8.3.a: Students know the

structure of the atom and know it is composed of protons, neutrons, and electrons.

Science Standard 8.7.b: Students know each element has a specific number of protons in the nucleus (the atomic number) and each isotope of the element has a different but specific number of neutrons in the nucleus.

Inputatom: smallest particle of an element.electron: negatively charged particles in an

atom.nucleus: the central core of an atomproton: positively charged particles in an

atom’s nucleus.energy level: the specific amount of energy

an electron has.

Inputneutron: small particle in the nucleus of an

atom with no electrical chargeatomic number: the number of protons in

the nucleus of an atom.isotope: atoms of the same element that

have different numbers of neutrons.mass number: the sum of the protons and

neutrons in the nucleus of an atom.

InputDevelopment of Atomic Theory

Atomic theory grew as a series of models that developed from experimental evidence. As more evidence was collected, the theory and models were revised.

The atom is the smallest particle of an element.Around 430 B.C., a Greek philosopher,

Democritus, proposed the idea that matter is formed of small pieces that could not be cut into smaller parts. He used the word atomos which means “uncuttable” for those smallest pieces.

Input & ModelingDalton’s Atomic Theory

Dalton thought that atoms were like smooth, hard balls

that could not be broken into smaller pieces.

Input & ModelingDalton’s Atomic Theory

All elements are composed of atoms that cannot be divided.

All atoms of the same element are exactly alike and have the same mass. Atoms of different elements are different and have different masses.

An atom of one element cannot be changed into an atom of a different element. Atoms cannot be created or destroyed in any chemical change, only rearranged.

Every compound is composed of atoms of different elements, combined in a specific ratio.

Input & ModelingThomson’s Atomic Theory

Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere.

In 1897, English scientist J.J. Thompson found that atoms contain negatively charged particles.The negatively charged particles later became known as electrons.

Input & ModelingRutherford’s Atomic Theory

According to Rutherford’s model, an atom was mostly empty space.

In 1911, Ernest Rutherford found evidence that countered Thompson’s model.

His team discovered the positive charge (proton) in an atom is clustered in the center (nucleus).

Input & ModelingBohr’s Atomic Theory

In 1913, Niels Bohr, a Danish scientist, suggested that electrons

move in specific orbits around the nucleus of an atom.

Input & ModelingCloud ModelIn the 1920’s, scientists determined that electrons

do not orbit the nucleus like planets, but rather could be anywhere in a cloudlike region.

An electron’s movement is

related to its energy level, or

the specific amount of energy

it has.Electrons of different energy

levels are likely to be found in

different places.

Input & ModelingThe Modern Atomic Model

In 1932, English scientist James Chadwick discovered another particle, the neutron, in the nucleus of atoms.

Input & ModelingThe Modern Atomic Model

At the center of the atom is a tiny, massive nucleus containing protons and neutrons.

Surrounding the nucleus is a cloudlike region of moving electrons.

The particle was difficult to detect because it has no charge.

InputParticles in an Atom

An atom is composed of positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are about equal in mass. An electron has about 1/2,000 the mass of a proton or neutron.

InputIsotopes

Atoms of all isotopes of carbon contain six protons and six electrons, but they differ in their number of neutrons. Carbon-12 is the most common isotope.

What is located in a cloudlike region surrounding the nucleus in the modern atomic model?

Check forUnderstanding

electrons

According to Dalton, all elements are composed of atoms that cannot be ___.

divided

Answer #1-4Guided Practice

Independent PracticeFinish the worksheet.Complete the extension.

EXTENSION Write a detailed SUMMARY of the section and

complete the UNANSWERED QUESTIONS section of your notes.

Choose two of the remaining Depth & Complexity ICONS in your notes and explain how they relate to this section.

Finish the Development of Atomic Theory Timeline Booklet.