Electron
Proton
Defining the atom:
-An atom is the smallest particle of an element that retains its identity in a chemical reaction.

Democritus believed that atoms were indivisible and indestructible.
Dalton s atomic theory was the first theory to relate to chemical changes to events at the atomic level.

1.) All matter is made of atoms. Atoms are indivisible and indestructible.
2.) All atoms of a given element are identical in mass and properties.
3.) Compounds are formed by a combination of 2 or more different kinds of atoms.
4.) A chemical reaction is a rearrangement of atoms.

1.) How did Democritus characterize atoms?
2.) In your own words state the main ideas of Dalton’s
Atomic Theory.
3.) According to Dalton’s theory, is it possible to convert atoms of one element into atoms of another?
Explain.
4.) What Charge does a neutron have? Proton? And electron?
5.) What is an atom?
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Structure Of An Atom
Three types of subatomic particles:
Thomson 1897 : performed experiments that involved passing electric current through gases at low pressure. The result was a cathode ray or
glowing beam. Thomson concluded that a cathode ray is a stream of tiny negatively charged particles moving at high speed. He later named them electrons and concluded that electrons must be parts of the atoms of all elements.
Thomson's plum pudding model demonstrated corpuscles scattered randomly throughout the atom like plums scattered throughout the pudding.

Rutherford's gold foil experiment yielded evidence of the atomic nucleus. Rutherford and his coworkers aimed a beam of alpha particles at the sheet of gold foil surrounded by a fluorescent screen. Most of the particles passed through the foil with no deflection at all. A few particles were greatly deflected. Rutherford concluded that most of the alpha particles pass through the gold foil because the atom is mostly empty space. The mass and positive charge are concentrated in a small region of the atom. Rutherford called this the nucleus. Particles that closely approach the nucleus are deflected.

Rutherford proposed later that the atom is mostly empty space. He called the region the nucleus. (a tiny central core of an atom and is composed of protons and neutrons) Rutherford’s atomic model is known as the nuclear atom. In the nuclear atom, the protons and neutrons are located in the nucleus.
The electrons are distributed around the nucleus and occupy almost all of the volume of the atom.

1.) What are three types of subatomic particles?
2.)How does the Rutherford model describe the structure of atoms?
3.) What are the charges and masses of the three subatomic particles?
4.) Describe the plum pudding model.
5.) How did Rutherford's model of the atom differ from
Thomson’s?
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Distinguishing Among Atoms tomic Number- of an element is the number of protons in the nucleus of an atom of that element. The atomic number identifies an element. ass number- the total number of protons and neutrons in an atom.
Elements are different because they contain different number of protons.
Au is the chemical symbol for gold.
How many electrons does a gold atom have
197
79

Atomic massthe weighted average of the masses of the isotopes of an element. calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.
Are atoms that have the same number of protons but different numbers of neutrons.
Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.

Period : each horizontal row of the periodic table
Group : Each vertical column of the periodic table
A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties.
-A periodic table allows you to easily compare the properties of one element ( or group of elements) to another element (or group of elements)

1.) What distinguishes the atoms of one element from the atoms of another?
2.)What equation tells you how to calculate the number of neutrons in an atom?
3.)How do the isotopes of a given element differ from one another?
4.) How is atomic mass calculated?
5.)What makes the periodic table such a useful tool?
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