The Structure of an Atom Flashcards
Basic structural unit of an element that retains chemical properties
Atom
Consists of different subatomic particles
Atom
4 subatomic particles
- electrons
- nucleus
- protons
- neutrons
Negatively charged subatomic particle (outside nucleus)
Electron (e-)
Small and dense center of an atom
Nucleus
Positively charged subatomic particle
Proton (p+)
Uncharged subatomic particle
Neutron (n0)
A pure substance that cannot be broken down into simpler substances by a chemical reaction
Element
atoms of the same element having different masses
isotopes
The weighted average of the masses of all the isotopes that make up the element
Atomic mass
A theory based on the law of conservation of mass and Law of definite proportions
John Dalton’s Atomic theory
- All matter consists of tiny particles called atoms
- An atom cannot be created, divided, destroyed, or converted to any other type of atom
- Atoms of a particular element have identical properties
John Dalton’s Atomic Theory
- Atoms of different elements have different properties
- Atoms of different elements combine in simple whole-number ratios to produce compounds (stable combinations of atoms)
- Chemical change involves joining, separating, or rearranging atoms
John Dalton’s Atomic Theory
4 individuals who found evidences of subatomic particles
- J.J Thomson (1897)
- Robert Millikan (1910)
- Ernest Rutherford (1897-1920)
- James Chadwick (1920 - 1932)
- Cathode ray tube experiment
- Cathode rays are stream of negative
particles of energy - discovered electrons
J.J Thomson (1897)
- oil-drop experiment
- identified the magnitude of mass and charge of the electron
Robert Millikan (1910)
- “Gold Foil Experiment” lead to the understanding of the nucleus
- Most alpha particles pass through the foil without being deflected
Ernest Rutherford (1897 - 1920)
- Some particles were deflected, a few even directly back to the source
- interpreted that an atom is empty space and most of the mass and positive charge (protons) must be located at the small and dense region (nucleus).
Ernest Rutherford (1897 - 1920)
- bombarded Beryllium with alpha particles from the natural radioactive decay of Polonium
- concluded that the unusually penetrating radiation consisted of uncharged particles having (approximately) the same mass as a proton (neutrons).
James Chadwick (1920 - 1932)
- In 1913, _____ proposed a theory for hydrogen atom.
- Atoms can absorb and emit energy via promotion of electrons to higher energy levels and relaxation to lower levels
Neils Bohr’s Atomic Theory
- Electrons are found in allowed energy levels (quantized energy levels, or orbits)
- Energy that is emitted upon relaxation is observed as a single wavelength of light
Neils Bohr’s Atomic Theory
light emitted when a substance is excited by an energy source
Emission spectrum
- Emission spectrum - light emitted when a substance is excited by an energy source
- Spectral lines are a result of electron transitions between allowed levels in the atoms
- The emission spectrum of hydrogen led to the modern understanding of the electronic structure of the atom.
Neils Bohr’s Atomic Theory
An atomic Model proposed by Erwin Shrodinger (1887 - 1961)
Quantum Mechanical Model
