Atomic structure Flashcards
Describe how Dalton’s ideas about atoms have changed.
Dalton’s model (1803): Atoms are solid, indivisible spheres.
Thomson (1897): Discovered the electron, proposing the “plum pudding” model with electrons embedded in a positively charged sphere.
Rutherford (1911): Discovered the nucleus through the gold foil experiment, showing atoms have a small, dense, positively charged center.
Bohr (1913): Proposed that electrons orbit the nucleus in defined energy levels.
Modern model: Atoms consist of a nucleus containing protons and neutrons, with electrons in surrounding orbitals.
Describe how the subatomic particles are arranged in an atom.
Protons and neutrons are found in the nucleus at the center of the atom.
Electrons are arranged in shells (energy levels) around the nucleus.
Explain how atoms of different elements are different.
Atoms of different elements have different numbers of protons.
The number of protons, called the atomic number, defines the element.
Different elements also have varying numbers of neutrons and electrons, giving them distinct properties.
Recall the charges and relative masses of the three subatomic particles.
Proton: Charge = +1, Relative mass = 1
Neutron: Charge = 0, Relative mass = 1
Electron: Charge = -1, Relative mass ≈ 1/1836 (negligible)
Explain why all atoms have no overall charge.
Atoms have equal numbers of protons (positive charge) and electrons (negative charge).
The opposite charges cancel out, so the atom has no overall charge.
Describe how the size of an atom compares to the size of its nucleus.
The nucleus is extremely small compared to the overall size of the atom.
The nucleus is about 1/100,000 the size of the atom.
State where most of the mass of an atom is found.
Most of the mass of an atom is found in the nucleus, which contains protons and neutrons.
State the meaning of atomic number.
The atomic number is the number of protons in the nucleus of an atom.
It defines the element.
State the meaning of mass number.
The mass number is the total number of protons and neutrons in an atom’s nucleus.
Describe how the atoms of different elements vary.
Atoms of different elements have different numbers of protons.
The number of neutrons and electrons can also vary, but the atomic number (protons) distinguishes one element from another.
State the number of electrons in an atom from its atomic number.
In a neutral atom, the number of electrons is equal to the atomic number (which is the number of protons).
Calculate the numbers of protons, neutrons, and electrons using atomic and mass numbers.
Protons = Atomic number
Electrons = Atomic number (for neutral atoms)
Neutrons = Mass number - Atomic number
State what is meant by an isotope.
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
This means they have the same atomic number but different mass numbers.
Identify isotopes from information about the structure of atoms.
Isotopes can be identified by their different mass numbers.
Example: Carbon-12 and Carbon-14 are isotopes of carbon, with 6 protons but different numbers of neutrons.
Calculate the numbers of protons, neutrons, and electrons using atomic numbers and mass numbers.
Example: For Carbon-14 (atomic number 6, mass number 14):
Protons = 6
Electrons = 6 (if neutral)
Neutrons = 14 - 6 = 8
