4th Quarter Exam in Science 9

• Atom - is the building block of matter.
• Molecule - are 2 atoms combined.
• Matter - anything that takes up space and has mass.
• Chemical bond - is an attractive force that binds atoms together. The properties of the atoms determine the type of bonds that hold them together.
• Invisible Particle (1803) - John Dalton proposed that the invisible unit of matter is the atom.
• Plum Pudding Model (1904) - J.J. Thomson discovered electrons, which were believed to reside in a sphere of uniform positive charge.
• Planetary Model (1911) - Ernest Rutherford demonstrated the presence of a positively charged nucleus.
• Atomic Model (1913) - Bohr proposed the existence of orbits around the nucleus in which electrons can be found.
• Quantum Mechanical Model (1926) - in the modern model, electrons occupy regions of space or orbitals around the nucleus.
• Democritus - proposed the atomic theory.
• John Dalton - he proposed that the indivisible unit of matter is the atom.
• J.J. Thomson - he discovered the electrons.
• Ernest Rutherford - discovered the nucleus. He performed the “gold-foil experiment” or “alpha-scattering experiment.”
• Nucleus - a dense positively charged region located at the center.
• Rutherford’s model - according to ___, an atom has a nucleus many times smaller than the atom itself, while the electrons occupy the remaining space. His model was described as the solar system or the planetary model of the atom.
• Niels Bohr - a student of Rutherford who proposed another model of the atom. This model used the concept of quantization of energy of electrons in the atom. He developed a quantum model of the electron cloud of an atom using data from the hydrogen spectrum in which electrons are located in a definite orbit.
• Energy levels - the possible orbits.
• Quantized - means that only specific values are possible.
• Niels Bohr - won a Nobel Prize in Physics for his contributions to the understanding of the structure of atoms.
• Energy level 1 = Maximum no. of electrons 2
• Energy level 2 = Maximum no. of electrons 8
• Energy level 3 = Maximum no. of electrons 18
• Energy level 4 = Maximum no. of electrons 32
• Electron Configuration - shows the specific arrangement of electrons in the orbitals of an atom.
• Energy level - the principal shell which is a positive nonzero integral value.
• Subshell/sublevel - the letter that describes the orbital type.
• Superscript - shows the number of electrons in a specific subshell.
• Subshell s = No. of electrons ≤ 2
• Subshell p = No. of electrons ≤ 6
• Subshell d = No. of electrons ≤ 10
• Subshell f = No. of electrons ≤ 14