Chemisty Grade 9 2nd Quarter

• Atoms are composed of a nucleus, protons, neutrons, and electrons.
• Atoms are the tiny particles that serve as the building blocks of matter.
• Democritus, around 500 BC, proposed that matter could not be divided indefinitely, leading to the idea that atoms are indestructible.
• The Greek word for "indivisible" is atomos.
• Aristotle, around 350 BC, proposed that matter is made up of elements such as fire, water, air, and earth.
• John Dalton, in 1803, proposed an atomic theory based on experimentation, not on pure reason.
• All matter is made of atoms, according to Dalton's atomic theory.
• Atoms of an element are identical, according to Dalton's atomic theory.
• No atoms is created nor destroyed, according to Dalton's atomic theory.
• Atoms of different elements combine in constant ratios to form compounds, according to Dalton's atomic theory.
• The "Billiard Ball" Model suggests that atoms are solid and indivisible spheres.
• Joseph John Thomson, in 1898, discovered the negatively charged particle-electron using a cathode ray tube.
• The "Plum Pudding Model" suggests that atoms are composed of subatomic particles that are electrically charged embedded in a positively charged mass.
• Ernest Rutherford, in 1911, proposed that atoms are mostly empty space and that negative electrons orbit a positive nucleus.
• Neils Bohr, in 1913, proposed that electrons are arranged in concentric circular orbits around the nucleus.
• Arnold Sommerfeld, in 1913, proposed that electrons moved in elliptical orbits.
• Erwin Schrodinger, in 1926, proposed that electrons are moving and around in random patterns.
• The "Quantum Mechanical Model" is a mathematical model used to describe the behavior of electrons.
• The number of protons is equal to the atomic number (Z).
• The nucleus contains protons and neutrons.
• Protons are positively charged particles, neutrons have no charge, and electrons are negatively charged particles.
• Atomic Number - the total number of protons found inside the nucleus
• Mass Number - the sum of the number of neutrons and protons present in the atom
• Nucleus ‐ a very dense region consisting of protons & neutrons at the center of an atom was discovered by Ernest Rutherford in 1911.
• Electron ‐ discovered by Joseph John Thomson
• Proton ‐ Eugene Goldstein
• Neutron ‐ James Chadwick
• Red light has the longest wavelength and has the lowest energy.
• Violet light has the shortest wavelength and has the highest energy.
• Analysis of light given off by the vapors of elements can be done more precisely with an instrument called spectroscope.
• These orbits are also known as "shells" or "energy levels" and are assigned each a number: n=1, n=2, n=3, etc or letters (K, L, M, N, O, etc).
• If the electron received extra energy, it can jump into a higher energy level, this is also called excited state.
• The electron in the excited state can return to its original lower energy level or ground state by releasing discreet amount of energy in the form of light.
• An atomic orbital is the region around the nucleus where the electron is most likely to be found.
• Energy sublevels as shown by the finer lines in the atomic emission spectra of elements.
• Aufbau's Principle is also known as the "building-up" principle, states that electron's occupy orbitals in order of increasing energy.
• Pauli's Exclusion Principle is when electrons occupying the same orbital must have opposite spin.
• Hund's rule of Multiplicity is when electrons enter a sublevel with more than one orbital, they will spread out to the available orbitals with the same spin before pairing.
• Sodium Nitrate (NaNO3) — Sodium — Yellow Barium Chloride (BaCl2) — Barium — Green Barium Nitrate (Na₂NO3) — Barium — Green Calcium Chloride (Ca₂Cl) — Calcium — Orange Copper Chloride (CuCl) — Copper — Blue Lithium Carbonate (Li2CO3) — Lithium — Red
• Mass Number - The sum of the number of neutrons and protons in the nucleus.