24 Questions
What did Joseph John Thompson discover in 1898?
Atoms could eject a far smaller negative particle called an ELECTRON
Who developed the idea of atoms and what did he call them?
Democritus; ATOMA (greek for indivisible)
According to John Dalton, what was all matter made up of?
Tiny spheres called ATOMS
What did Rutherford propose after his experiment with the gold foil?
A more detailed model of the atom with a central nucleus
Write the electronic configuration for Calcium (Ca) with atomic number 20.
2,8,8,2
Describe Thompson's Plum Pudding model of the atom.
An atom made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge
What was the outcome of Rutherford's famous experiment with gold foil?
Most helium nuclei passed through, but some were deflected and others bounced straight back
Draw the Dot & Cross diagram for Oxygen (O) with atomic number 8.
X O X X O X
Explain the relationship between the Atomic Number and the number of Protons in an atom.
The Atomic Number of an atom equals the number of protons in its nucleus.
Define the Atomic Mass of an atom and how it is calculated.
The Atomic Mass of an atom is the sum of the number of Protons and Neutrons in the nucleus.
How do Electrons orbit the nucleus in an atom?
Electrons orbit the nucleus in shells.
Explain the principle that the number of Protons in an atom is equal to the number of Electrons.
In an atom, the number of Protons always equals the number of Electrons.
What did Niels Bohr add to Rutherford's model of the atom?
Electrons in orbits
Explain the concept of atomic number.
Number of protons in an atom
How are electrons arranged in an atom according to atomic structure?
In energy levels or shells around the nucleus
What is the maximum number of electrons that can be in the third shell of an atom?
8 electrons
What is the charge and mass of a neutron?
No charge, mass of 1
How are elements represented numerically in electronic configuration?
By the number of electrons in their shells and the number of shells
Who is credited with overseeing the famous experiment where helium nuclei were fired at a piece of gold foil?
Ernest Rutherford
What was the outcome of Rutherford's experiment with the gold foil?
Some helium nuclei were deflected and others bounced straight back.
What did Rutherford propose as a result of the evidence from the gold foil experiment?
A more detailed model with a central nucleus
Describe John Dalton's theory about the structure of matter.
Tiny spheres that could bounce around with perfect elasticity
What did Joseph John Thompson discover about atoms in 1898?
Atoms could sometimes eject a far smaller negative particle called an electron
Explain Thompson's Plum Pudding model of the atom.
An atom made up of electrons scattered unevenly within a sphere of positive charge
Study Notes
Atomic Structure
- Atomic Number: number of protons in an atom's nucleus
- Atomic Mass: number of Protons + Neutrons in an atom's nucleus
- Number of Protons = Number of Electrons
- Electrons orbit the nucleus in shells
- Each shell can carry a set number of electrons
Electronic Configuration
- Elements are represented numerically by the number of electrons in their shells and number of shells
- e.g., Nitrogen: 2 in 1st shell, 5 in 2nd shell = 2, 5, 2+5=7, N 7 14
Dot & Cross Diagrams
- Elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells
- e.g., Nitrogen: X X N XX X X N 7 14
Atomic Structure Models
- Rutherford's Model: central nucleus with electrons in orbits
- Bohr's Model: electrons in orbits around the nucleus, each orbit with a set number of electrons
- Plum Pudding Model: electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge
History of the Atom
- 460 BC: Democritus develops the idea of atoms
- 1808: John Dalton suggests that all matter is made up of tiny spheres called atoms
- 1898: Joseph John Thompson discovers electrons
- 1904: Thompson develops the idea of an atom with electrons scattered unevenly within an elastic sphere
- 1910: Rutherford's experiment leads to a more detailed model with a central nucleus
- 1913: Niels Bohr refines Rutherford's idea by adding electrons in orbits
Test your knowledge of electronic configurations and dot & cross diagrams by providing the electronic configuration for elements such as Ca, Na, Cl, Si, O, and B, and drawing dot & cross diagrams for various elements and compounds. Practice identifying the number of electrons in each shell and representing them using dots and crosses.
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