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| Term | Definition |
|---|---|
| Element | A substance that only contains one type of an atom. The type of atom is determined by the amount of protons it contains. |
| Periodic Table | A diagram that shows all the elements that are known in the universe. They are organized by types in groups (columns) and periods (rows). |
| Atomic Number | The amount of protons an element contains. Elements are listed from left to right and top to bottom from the smallest number to the largest. |
| Atomic Mass | The mass of an atom, and is often expressed in the non-SI unit atomic mass unit (amu) or unified mass (u) or dalton (symbol: Da), where 1 amu or 1 u or 1 Da is defined as 1⁄12 of the mass of a single carbon-12 atom, at rest. |
| Atom | A particle that contains a nucleus that can contain both protons and neutrons, and electrons that move around it. |
| Subatomic particle | A particle that is smaller than an atom. Examples include, protons, neutrons, electrons, and photons. |
| Ion | An atom that has less or more electrons than protons in its nucleus. Cation An ion that has an overall positive charge, so it has less electrons than protons. Anion An ion that has an overall negative charge, so it has more electrons than protons. |
| Isotope | An atom with more or less neutrons than it would normally have. |
| Core Electrons | Electrons that are between the nucleus and the valence electrons. |
| Valence Electrons | The farthest electrons from the nucleus. The number is determined by the one’s digit of the group and element is in the Periodic Table (the d-block is an exception). |
| Orbital | An area where an electron occupies and defines where it can go at any given moment. |
| Shell | Defines how far an electron is from the nucleus and its energy level, the further away an electron is from the nucleus, the lower its energy level. A shell can contain multiple orbitals. |
| Nuclear Charge | The charge the nucleus has over all, or how much of a positive charge it has. The higher the nuclear charge, the less ionization energy there is. |
| Shielding/Screening | The action of core electrons pushing a valence electron from the nucleus while the protons in the nucleus pull the electron closer to the nucleus, keeping the electron in the outer shell. The further right you go on the Periodic Table, the smaller the atom gets and the closer the valence electrons get to the nucleus. The higher the shielding/screening there is, the less ionization energy there is. |
| Ionization Energy | The required amount of energy required to remove a valence electron, measured in kJ/mol. This decreases the lower you go on the Periodic Table and increases the further right you go. |
| Effective Nuclear Charge | The total amount of force an electron feels towards the nucleus. The greater the number, the greater the pull the nucleus has. This is affected by the nuclear charge, shielding/screening, and distance of the electron from the nucleus. Equation: Zeff: Effective Nuclear Charge Z: Number of Protons S: Number of Core Electrons, this does not have to be an integer. The farther away the electron is to the nucleus, the larger the ionization energy is. |
| Electron Affinity | The degrees to how much a given atom wants new electrons, how much they want electrons. The energy change that occurs when adding a new electron. |
| Electronegativity | A measure of an atom’s ability to attract shared electrons to itself, how badly it wants to “hog” electrons. On the Periodic Table, electronegativity generally increases as you move from left to right across a period and decreases as you move down a group. Something that is not very Electronegative is called Electropositive. |
| mol/mole | An Avogadro’s Constant amount of atoms given a sample or compound. m: Mass amu: Atomic Mass Unit To find the grams of a sample or compound. g: Grams amu: Atomic Mass Unit |
| Avogadro’s Constant | How many atoms are in one mol of a substance or compound, which is |
| Aufbau Principle | The order in which electrons fill the shells of an atom.** |
| Coulomb’s Law | Determines how atoms move depending on the charge of the atoms themselves. F: Force kₑ: Coulomb constant, q: Atoms involved r: Radius between the atoms |