Matter & The Atom. Matter The term matter describes all of the physical substances around us Anything that has mass and volume (takes up space)

Matter &The Atom

MatterThe term matter describes all of the physical substances around us

Anything that has mass and volume (takes up space)

The Universe is made up of matter and energy (light, sound, and heat are not made of matter)

Matter is made of atoms

Atoms are the building blocks of matter

An atom is the smallest whole particle of matter

Sub-atomic particles are tiny particles that make up an atom

Models

Models are often used for things that are too small or too large to

be observed or that are too difficult to be understood easily

ModelsIn the case of atoms, scientists use large models to explain something that is very small How small are atoms? http://learn.genetics.utah.edu/content/begin/cells/scale/

Models of the atom were used to explain data or facts that were gathered experimentally.

So, these models are also theories

Early Models of the Atom Democritus

He asked: “What would happen if you took something (like a tree) and kept breaking it into smaller and smaller pieces?

Would it still be a piece of a tree?

Could you keep breaking it?

He concluded: Eventually you would get to a size that could no longer be broken.

This would be an indivisible piece

Greek word: atomos = indivisible

Thus: ATOM

(442 B.C.)

Early Models of the Atom John Dalton

(1803)All elements are composed of indivisible particles. Atoms of the same element are the sameAtoms of different elements are different. Different elements are atoms with different masses

Early Models of the AtomJ.J. Thomson

(1897)

Found negative and positive charges

Plum pudding model

Atom made of a positively charged material with the negatively charged electrons scattered through it.

Early Models of the Atom Ernest Rutherford

(1899)

Mostly empty space

Small, positive nucleus

Contained protons

Negative electrons scattered around the outside

Early Models of the Atom Niels Bohr (1915)

Electrons are small and negatively charged

Electrons move in definite orbits around the nucleus (energy levels)

Protons are in the nucleus and the nucleus is small compared to the atom

Early Models of the Atom James Chadwick

(1932)

Discovered the neutron

Modern Model of the AtomThe electron cloud

Spherical cloud of varying density Varying density shows where an electron is more or less likely to be

Atomic Structure

Nucleus – Protons

– Neutrons

Electrons

Atomic Structure

Nucleus The center of the atom– Contains protons and neutrons

All particles are inside or around the nucleus

Atomic Structure

Electrons (e-)Tiny, very light particles – Smallest subatomic particle

Have a negative electrical charge (-)

Found in a cloud outside of the nucleus

Orbits in energy levels

Atomic Structure

Protons (p+) Located in the nucleus of the atom 

Much larger and heavier than electrons

Protons have a positive charge (+)

Number of protons is different for each element. If the number of protons changes, the element changes.

Atomic Structure

Neutrons (n0)Located in the nucleus of the atom 

Large and heavy like protons, a bit bigger than a proton

Neutrons have no electrical charge (neutral)

Relative size of sub-atomic particles

Atomic Structure

proton (p+)

neutron (no)

electron (e-)

Describing Atoms

Atomic Number = number of protons

– In a neutral atom, the # of protons = the # of electrons

– All atoms want to be neutral (no electrical charge)

Element Atomic # # protons

Hydrogen 1 1

Gold 79 79

Oxygen 8

Iron 26 26

Lead 82

Helium 2

Sodium 11 11

Sulfur 16

Describing Atoms

Atomic Mass Number - sum of the number of protons plus neutrons.

– Electrons are so tiny that their mass isn’t enough to affect the atomic mass

Measured in Atomic Mass Units (amu)

IsotopesIsotope – when an atom has a different number of neutrons than other atoms of the same element

–Example: 2 Oxygen Atoms, one has 8 neutrons one has 9.

Isotopes, continued

The number of protons for a given atom never changes.

The number of neutrons can change. 

Two atoms with different numbers of neutrons are called isotopes

Isotopes have the same atomic #

Isotopes have different atomic Mass #’s