A Greek philosopher who theorized that all matter could be reduced to particles that could not be divided, which he described as "atomos."
greek word for atom- means not able to be divided
All atoms were small, hard particles and made of a single material formed into different shapes and sizes.
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.
the smallest particle into which an element can be divided and still be the same substance
Who was right, Democritus or Aristotle?
Elements combinte in certain proportions based on mass to form.....
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 of the same element are exactly _______, according to Dalton.
Atoms are small particles that can not be ________ according to Dalton.
created, divided or destroyed.
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.
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
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.
When this happened in the gold foil experience, it helped Rutherford discover the nucleus.
The center of the atom which contains the protons and neutrons
a region around the nucleus of an atom where electrons are likely to be found
This is the extremely dense center of the atom.
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.
Most current atomic theory is represented by this.
The electron cloud model.
Dalton experimented with many ___________ substances
Who discovered the electron?
Dalton based his theory on observations about how.....
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
protons have a mass of about
The particles of a nucleus that have no electrical charge are....
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
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
a subatomic particle that has no charge and that is found in the nucleus of an atom
the most abundant element in the universe.
It makes more than 1,800 electrons to equal the mass of
The charges of protons and electrons are
opposite but equal
atoms usually have no charge, so they are
if an atom has an unequal number of electrons and protons, it is
a charged particle called an 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
The simplest atom, it has just one proton and one electron.
This atom has two protons, two neutrons, two electrons.
The number of protons in the nucleus of an atom
All atoms of an element have .....
the same atomic number.
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.
unstable isotopes are this.
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.
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?
If you have 5 protons and 5 neutrons, what is the atomic number?
If you have 5 protons and 6 neutrons, what is the mass number?
If you have 6 protons and 6 neutrons, what is the mass number?
If you have 6 protons and 6 neutrons, what is the atomic number?
If you write hydrogen-1, what was the 2 represent?
If you write hydrogen-2, what does the 2 represent?
If you write carbon-12 and you know the atomic number for carbon is 6, how many neutrons does it have?
If you write carbon-10 and you know the atomic number for carbon is 6, how many neutrons does it have?
If you write carbon-14 and you know the atomic number for carbon is 6, how many neutrons does it have?
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?
What is the atomic mass of gallium if it is 60% gallium-69 and 40 gallium-71?
What is the atomic mass of silver if it is 52% silver-107 and 48% silver-109?
What is the atomic mass of an element "sample" which is 25% sample-8 and 75% sample 9?
What is the atomic mass of an element "sample" which is 75% sample-8 and 25% sample 9?
What is the atomic mass of an element "sample" which is 50% sample-8 and 50% sample 9?
What is the atomic mass of an element "sample" which is 50% sample-6 and 50% sample 9?
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.
This force within atoms helps to keep the nucleus together.
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
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......
Ordinary-sized objects are made up of
very large numbers of atoms
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