chemistry

• In the periodic table, the vertical columns are called groups. They indicate how may electrons the element has on its valence shell.
• In the periodic table, the horizontal rows are called periods. They indicate how many electron shells an element has.
• Atoms are made of protons, neutrons and electrons.
• The weight of all other atoms is compared to carbon.
• An atomic mass unit is defined as accurately 1/12 the mass of a carbon-12 atom.
• Atomic mass unit (AMU), in physics and chemistry, a unit for expressing masses of atoms, molecules, or subatomic particles.
• The mass number is defined as the total number of protons and neutrons in an atom. Mass number = number of protons+ number of neutrons.
• The atomic number is the number of protons in the nucleus of an atom. Atomic number = Number of protons.
• The atomic number is the number of protons in an element, while the mass number is the number of protons + neutrons in an element.
• Amount of substance(n) is measured in moles(mol).
• The amount of substance means the amount of matter in a given volume of a substance.
• Amount of substance = moles x Avogadro's constant (6.022 x 10^23)
• moles in a substance = the mass/molar mass
• All substances can be divided to two groups: pure substances and mixtures.
• Pure substances can also be divided into two groups: chemical elements and compounds.
• Mixtures can be divided into two groups: homogeneous mixtures and heterogeneous mixtures.
• Homogenous mixtures appear the same throughout, while heterogenous mixtures are visually distinguishable.
• Elements contain only one type of atom, they are all the same.
• Compounds contain at least two types of atoms, but always in the same proportion.
• Mixtures consist of at least two different pure substances.
• Components can be mixed in different porportions.
• Chemical reactions involve changes in matter where reactants (starting materials) produce products (new substances).
• Concentration as percentage: m%(component) = m(component)/m(mixture) x 100% Vol%(component)= V(component)/V(mixture) x 100%
• In chemistry, concentration is most often expressed in molarity by units of molar (M), which is moles per liter solution. (mol/L)
• An anion is an ion with negative charge, meaning it has more electrons than protons. Anions are formed when an atom gains one or more electrons: the gain of the negatively-charged electron(s) results in an overall negative charge.
• Cations are ions that are positively charged. Anions are ions that are negatively charged. Ions are charged atoms or molecules. If a balanced atom loses one or more electrons, it will become a positively charged cation
• Cations are ions that are positively charged. Anions are ions that are negatively charged.
• An ion is an atom or molecule that is charged due to a difference in number of electrons and protons.
• Anions and cations are held together by a really strong force called ionic bonds.
• The periodic table organizes elements into groups based on their atomic structure and properties.
• An exothermic process releases heat, causing the temperature of the immediate surroundings to rise. An endothermic process absorbs heat and cools the surroundings.
• An exothermic process releases heat, causing the temperature of the immediate surroundings to rise. An endothermic process absorbs heat and cools the surroundings.
• Phase changes: Solid: network of bonds, maintains its shape. Liquid: some bonds have been broken, fills the bottom of the container. Gas: No bonds between particles, fills the entire container.
• The higher the melting point is, the stronger the bonds are between the atoms.
• Strength of bond depends on: type of bonding, strength of charges, and distance between charges.
• Macromolecular crystal = a crystalline solid in which the atoms are all linked together by covalent bonds.
• Molecular substance = a substance with two or more atoms, joined together by covalent bonds.
• Intermolecular bond = caused by the attractive forces between the positive end of one molecule and the negative end of another molecule.
• Types of intermolecular bonds: dipole-dipole bond, ion-dipole bond, hydrogen bond and London dispersion forces.
• The strength of intermolecular bonds depends on: type of molecular bonding, size of molecule(number of electrons, molar mass), amount of polar parts in the molecule and the shape of the molecule.