Dalton's Atomic Theory
“All matter consists of tiny, indivisible particles called ___.”
Atoms
Dalton revived Democritus’ concept of indivisible atoms.
Who discovered the electron’s charge-to-mass ratio?
J. J. Thomson
He did this using cathode ray experiments.
An atom is electrically neutral because it has equal numbers of ___ and ___.
Protons and electrons
Positive and negative charges balance out.
Provide the following for the atom:
Copper
1. Symbol
2. Atomic Number
3. Number of Protons
Cu
29
29
How many neutrons and protons are in the isotope of U-235?
# of protons: 92
# of neutrons: 143
Dalton’s theory states that atoms of the same element are identical in their ____.
Mass and properties
This explains why elements have consistent behavior in reactions.
Millikan’s oil-drop experiment measured the electron’s ____.
Charge
From this, the mass of the electron could be calculated.
The central part of the atom is called the ____
Nucleus
It contains protons and neutrons.
65Zn
Provide the following for the given above:
1. Atomic #
2. Mass #
3. # of neutrons
1. Atomic #: 30
2. Mass #: 65
3. # of neutrons: 35
Identify the element given the following information:
# of protons - 26
# of neutrons - 26
# of electrons - 24
Fe2+
This is an ionic form of iron. It has 2 less electrons than the neutral iron.
True or False:
According to Dalton, atoms of one element can be changed into atoms of another element through chemical reactions.
False
Dalton stated that atoms cannot be converted into another element by chemical means.
Rutherford’s gold-foil experiment showed that an atom’s positive charge is concentrated in the ____.
Nucleus
Most alpha particles passed through, but some deflected sharply, indicating a dense center.
True or False:
The mass of an atom comes mostly from electrons.
False
Most of the mass comes from protons and neutrons in the nucleus.
If an atom has 17 protons and 18 neutrons, its mass number is ____.
35
Atoms of the same element with different number of neutrons in the nuclei.
ISOTOPE
In what postulate/s we can associate MASS CONSERVATION?
Postulates 1 and 2
1. All matter consists of atoms, tiny indivisible units of an element that cannot be created or destroyed.
2. Atoms of one element cannot be converted into atoms of another element. In chemical reactions, the atoms of the original substances recombine to form different substances.
Who discovered the neutron?
James Chadwick
He found a dense, uncharged particle in the nucleus.
Fill in the blank: Protons have a ___ charge, while neutrons have ___ charge.
Positive; no (neutral) charge
This is why neutrons do not affect the net charge of an atom.
True or False:
The atomic number is always smaller than the mass number.
True
Mass number includes protons plus neutrons.
True or False:
Isotopes have the same number of neutrons but different numbers of protons.
False
Isotopes have the same number of protons but different numbers of neutrons.
TRUE OR FALSE?
All matter consists of atoms, tiny indivisible units of an element that cannot be created or destroyed.
Can this postulate be applied to the current discovery of atoms?
False.
Atoms can be divided into electrons, protons, and neutrons
Fill in the blank: The mass of a proton is approximately ___ times the mass of an electron.
1840
Protons are much heavier than electrons, but have an equal and opposite charge.
The number of protons in an atom is also called its ____
Atomic number
This number defines the element.
An atom with 30 protons and 35 neutrons has an atomic number of ____
30
Atomic number is based only on protons.
Fill in the blank: Isotopes of the same element have identical ____ properties
Chemical
They have the same number of protons and electrons.