Phys. Sci. Lesson 3-2

What are

atoms?

Lesson 3-2

● Identify an atom as the smallest

part of an element that can be

identified as that element.

● List the main parts of Dalton’s

atomic theory

Objective

Atoms

● elements can not be chemically broken

down into simpler substances

● if you took an element and cut it into

smaller and smaller pieces=

○ the smallest piece would be an atom

● an atom is the smallest part of an

element that can be identified as that
element

Democritus

● Democritus- Greek lived 2,400 years ago

● Asked “was it possible to divide matter

forever into smaller pieces”?

● NO

● But he & his students did not know

what atoms looked like

● They hypothesized:

○ atoms were small, hard particles that

were all made of same thing but
different shapes and sizes

○ they thought atoms were infinite in

number

○ they were always moving

○ they could be joined together

Dalton’s

Atomic Theory

● John Dalton-1800s- English chemist

● investigated the properties of gases

● he believed gases are individual

particles

○ his idea similar to Democritus

● his experiments led him to his atomic

theory of matter

● all elements are composed of atoms

● atoms cannot be divided or destroyed

● atoms of the same element are

exactly alike

● atoms of different elements are different

from each other

● atoms of 2 or more elements can join

together to form types of matter called:

compounds

● scientists no longer agree with

Dalton

● Dalton’s atomic theory was

beginning of modern theory of

atoms

Images of

Atoms

● you need a special tool to

see atoms to get a
picture of them

● scanning tunneling

microscope (STM)

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