Science - Introduction To Atoms

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Democritus

A Greek philosopher who theorized that all matter could be reduced to particles that could not be divided, which he described as "atomos."

atomos

greek word for atom- means not able to be divided

Democritus thought..

All atoms were small, hard particles and made of a single material formed into different shapes and sizes.

Aristotle

He disagreed with Democritus, believing that you would never end up with a particle that could not be cut.

Matter is made of......

Particles, which we call atoms.

Atom

the smallest particle into which an element can be divided and still be the same substance

Who was right, Democritus or Aristotle?

Democritus

Elements combinte in certain proportions based on mass to form.....

compounds

John Dalton

English chemist who developed the Atomic theory of matter through an experiment of gases. His theory states: A) All elements are composed of atoms and atoms can't be divided or destroyed. B) Atoms of the same element are exactly alike and atoms of different elements are different from each other. C) The atoms of 2 or more elements can join together to form types of matter called compounds.

All substances are made of _______, according to Dalton

atoms

Atoms of the same element are exactly _______, according to Dalton.

alike

Atoms are small particles that can not be ________ according to Dalton.

created, divided or destroyed.

J.J. Thomson

discovered the electron

What J.J. Thomson discovered about the atom

There are small particles inside the atom.

Cathode-Ray Tube Experiment

This was J.J. Thomson's famous experiment which discovered electrons.

Plum-pudding model

J.J Thomsons model of an atom, in which he thought electrons were randomly distributed within a positively charged cloud

Chocolate chip ice-cream model

What one might call today a model of an atom proposed by J.J. Thomson because he thought that electrons were mixed throughout an atom

Ernest Rutherford

From his gold foil experiments, he knew some substances give off + charged particles called alpha particles, most of the mass of an atom is in the nucleus, he reasoned that electrons in the atom are whirled around outside the nucleus, most of the atom is empty space

Discovered nucleus and the fact atoms are mostly empty space with a dense nucleus.

Earnest Rutherford

Deflected particles

When this happened in the gold foil experience, it helped Rutherford discover the nucleus.

nucleus

The center of the atom which contains the protons and neutrons

electron cloud

a region around the nucleus of an atom where electrons are likely to be found

This is the extremely dense center of the atom.

nucleus

Niels Bohr

discovered that electrons move around the nucleus in orbits called electron clouds. Also proposed that electrons

Proposed that electrons are located at certain distances from the nucleus.

Niels Bohr

Most current atomic theory is represented by this.

The electron cloud model.

Dalton experimented with many ___________ substances

different

Who discovered the electron?

J.J. Thomson

Dalton based his theory on observations about how.....

elements combine.

What are the particles of an atom?

protons, neutrons and electrons.

SI unit used to express the masses of particles in atoms is......

atomic mass unit

amu

atomic mass unit

protons have a mass of about

1 amu

The particles of a nucleus that have no electrical charge are....

neutrons.

neutrons are a little more massive than

protons. But the difference is small, they are still about 1 amu.

The small, dense positively charged center of the atom is called

the nucleus.

proton

A subatomic particle that has a positive charge and that is found in the nucleus of an atom

atomic mass unit

unit of mass for expressing masses of atoms or molecules

neutron

a subatomic particle that has no charge and that is found in the nucleus of an atom

hydrogen

the most abundant element in the universe.

It makes more than 1,800 electrons to equal the mass of

1 proton

The charges of protons and electrons are

opposite but equal

atoms usually have no charge, so they are

neutral

if an atom has an unequal number of electrons and protons, it is

a charged particle called an ion

ion

Atom that has a positive or negative charge

An atom which loses one or more electrons becomes a

positively charged ion

An atom which gains one or more electrons becomes a

negatively charged ion

There are more than _______ different elements

110

Hydrogen

The simplest atom, it has just one proton and one electron.

Helium

This atom has two protons, two neutrons, two electrons.

Atomic number

The number of protons in the nucleus of an atom

All atoms of an element have .....

the same atomic number.

Isotope

one of two or more atoms with the same atomic number but with different numbers of neutrons

The atomic number is the same for .....

all atoms of an element.

isotopes of hydrogen

They all have one proton, but they can have different numbers of neutrons in their nucleus.

radioactive

unstable isotopes are this.

Radioactive atoms

they spontanuously fall apart over time and they give off of energy

isotopes of an element generally.....

share most of the same chemical and physical properties.

How can you tell isotopes apart?

By looking at its' mass number.

Mass number

the sum of the number of neutrons and protons in an atomic nucleus

If you have 5 protons and 5 neutrons, what is the mass number?

10

If you have 5 protons and 5 neutrons, what is the atomic number?

5

If you have 5 protons and 6 neutrons, what is the mass number?

11

If you have 6 protons and 6 neutrons, what is the mass number?

12

If you have 6 protons and 6 neutrons, what is the atomic number?

6

If you write hydrogen-1, what was the 2 represent?

mass number

If you write hydrogen-2, what does the 2 represent?

mass number

If you write carbon-12 and you know the atomic number for carbon is 6, how many neutrons does it have?

6

If you write carbon-10 and you know the atomic number for carbon is 6, how many neutrons does it have?

4

If you write carbon-14 and you know the atomic number for carbon is 6, how many neutrons does it have?

8

Mass number - number of protons =

number of neutrons

atomic mass of an element

the weighted average mass of the isotope of that element

What is the atomic mass of boron if it is 20% boron-10 and 80% boron-11?

10.8

What is the atomic mass of gallium if it is 60% gallium-69 and 40 gallium-71?

69.7

What is the atomic mass of silver if it is 52% silver-107 and 48% silver-109?

107.9

What is the atomic mass of an element "sample" which is 25% sample-8 and 75% sample 9?

8.75

What is the atomic mass of an element "sample" which is 75% sample-8 and 25% sample 9?

8.25

What is the atomic mass of an element "sample" which is 50% sample-8 and 50% sample 9?

8.5

What is the atomic mass of an element "sample" which is 50% sample-6 and 50% sample 9?

7.5

forces in atoms

There are four of these.

gravitational force in atoms

this pulls objects together. Because particles in atoms are very small, the gravitational force within atoms is small.

electromagnetic force in atoms

This is the force which causes particles with the same charge to repel each other and causes particles with opposite charges to attract each other.

strong force

This force within atoms helps to keep the nucleus together.

weak force

This is an important force in radioactive atoms, helping to change neutrons into a proton and an electron.

Four forces at work in atoms

gravitational, electromagnetic,strong, weak

These are extremely small

atoms

The weighted average of the masses of natural isotopes in an element is

the atomic mass

Different isotopes of an element have.....

different numbers of neutrons in their nuclei

The number of protons in the nucleus of an atom is that atom's......

Atomic number

Ordinary-sized objects are made up of

very large numbers of atoms

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