Atomic Structure, Ions and Ionic Bonds

Atomic Structure and Ions

• Atoms are the smallest units of matter that retain a substance's properties.
• Elements consist of only one type of atom; a gold ring is made of gold atoms, a helium balloon contains helium atoms.

Structure of an Atom

• Electrons orbit in shells and have a negative charge and a mass of 1/1360.
• Neutrons are in the nucleus, have a neutral charge, and a relative mass of 1.
• Protons are in the nucleus, have a positive charge, and a relative mass of 1.

Drawing Atoms

• The atomic number indicates the number of protons in an atom.
• The number of electrons equals the number of protons.
• The mass number tells the number of protons plus neutrons in the nucleus.
• The first electron shell holds 2 electrons, and subsequent shells hold 8.

Ions and Ionic Bonds

• Atoms are electrically neutral when containing an equal amount of protons and electrons.
• Ions are electrically charged particles.
• A neutral atom that loses electrons becomes a positive ion.
• A neutral atom that gains electrons becomes a negative ion.

Atoms to Ions

• Atoms gain or lose electrons to achieve a full outer shell (8 electrons).
• Metals lose electrons to become positively charged cations.
• Nonmetals gain electrons to become negatively charged anions.

Metals and Nonmetals

• Metals lose electrons from their outer shell.
• Group 2 metals lose 2 electrons to become +2 ions.
• Nonmetals gain electrons to fill their outer shell.
• Group 7 atoms gain 1 electron to become -1 ions.

Ionic Bonding

• Atoms form ions by donating or accepting electrons through ionic bonding.
• Ionic bonding occurs between positive and negative ions.
• An ionic bond forms a weak electrostatic attraction between positive and negative ions.
• Ionic bonding happens when a metal reacts with a non-metal; the metal gives electrons to the non-metal.
• This typically occurs in groups 1, 2, 6, and 7, with some exceptions in group 3.
• After ionic bonding, atoms become positive and negative ions.
• They achieve the same electronic structure as a noble gas, having a full outer electron shell and held together by strong electrostatic attraction.
• A compound is a pure substance chemically bonded together from multiple elements, such as carbon dioxide and water

Naming Ionic Compounds

• An ionic bond is created when metal ions combine non-metal ions, involving electron transfer.
• Metals form positive ions (cations), and nonmetals form negative ions (anions). The cation is written first.
• In a binary compound of two elements, the second element's name changes to end in IDE.
• When a metal reacts with a nonmetal, it forms an ionic compound, also known as a salt.
• Metals are the first part of the salt's name, hence INE is changed to IDE.
• Converting INE to IDE, the cation is written first.
• For example, the name of the ionic compound of chlorine (anion/nonmetal) and sodium is sodium chloride.

Covalent Bonds

• In chemical formulas, a capital letter indicates the start of each new element.
• A lowercase letter following a capital letter means it is part of the same element, e.g., Cl for Chlorine.
• The formula HCl has two elements, hydrogen and chlorine.
• Co represents the single element cobalt.
• CO represents the compound carbon monoxide.
• Nonmetals react with each other to gain a full outer shell of electrons.
• Molecules are two or more atoms joined by a covalent bond.
• Each atom has a stable, full outer electron shell.
• The 7 diatomic elements are hydrogen, nitrogen, oxygen, fluorine, bromine, and iodine.
• Covalent bonding occurs only between nonmetals and requires atoms to overlap.
• Atoms only draw outer shell electrons and each atom donates the number of electrons needed for the covalent bond.
• Different symbols are used to represent the electrons on each atom.

Naming Covalent Compounds

• In the compound's name, the element furthest to the left on the periodic table is written first.
• In a binary compound, the second element’s name changes to end in IDE.
• Oxygen uses IDE; whenever oxygen is at the end of a binary compound, the ending changes to IDE.
• Use the molecular formula to find number of each type of atom using a prefix, except for one of the first element.
• Mono- is not added to the first element’s name, but it does apply to the second element.
• Drop the "a" or "o" at the prefix's end when the element name begins with a vowel; four oxygen atoms is tetroxide, not tetraoxide.
• The element that appears first is usually furthermost left on the periodic table, but carbon always appears first, for example, CH4..
• In a formula like NH#, hydrogen appears after nitrogen.

Classifying Compounds

• Crude oil is a mixture of compounds.
• A mixture contains two or more elements or compounds not chemically joined.
• Most compounds in crude oil are hydrocarbons.

Naming Alkanes

• The prefix of an alkane's name depends on the number of carbon atoms.
• All alkanes end in ANE.

Boiling Point of Hydrocarbons

• Boiling point increases with hydrocarbon size because the larger molecules are held together by weak intermolecular forces.
• More energy is needed to overcome these forces.

Viscosity of Hydrocarbons

• Viscosity measures how thick a liquid is.
• Low viscosity liquids like water flow easily.
• High viscosity liquids like treacle do not flow easily.

Exothermic and Endothermic Reactions

• Exothermic reactions release energy, causing the temperature to increase.
• Endothermic reactions absorb energy, causing the temperature to decrease.

Solutes, Solvents, and Solutions

• Water is a polar molecule, sharing electrons in covalent bonds between oxygen and hydrogen.
• Oxygen attracts electrons more strongly, resulting in a slight negative charge near the oxygen atom.
• Neutral molecules with positive and negative areas are polar molecules.
• Water molecules attract each other due to the positive end of one molecule attracting the negative end of another.

Precipitates

• When salts dissolve in water, they form positive or negative ions.
• Mixing solutions of two different salts can cause one of the positive ions to join with one of the negative ions to form a solid that does not dissolve, called a precipitate.
• Precipitation makes the solution opaque and sometimes colourful.

Solubility Rules

• Chemists use solubility rules to predict if a product will be soluble.
• If a product is insoluble, a precipitate forms.
• All nitrates and acetates are soluble.
• All salts of ammonium, lithium, sodium, and potassium are soluble.

Chemical Reactions

• Magnesium + Oxygen → Magnesium Oxide
• Reactants are the chemicals at the start of a reaction.
• Products are the chemicals at the end of the reaction.

Rates of Reactions

• All rates of reaction graphs level off when no more reactant is used or product made, indicating a reactant has run out.
• Collision is necessary for a reaction to happen, in which particles from the reactant chemicals must collide.

Collision Theory

• Particles must have enough energy to react upon collision.
• The minimum energy needed is the activation energy.

Concentration

• Higher reactant concentration leads to more particles in the same volume.
• This causes more frequent collisions and increases reaction rate.

Surface Area

• Increasing the surface area of a solid reactant increases the reaction rate.
• This can be achieved by using small chunks or a powder.

Temperature

• Increasing the temperature gives particles more kinetic energy making them move around faster.
• This leads to more frequent and energetic collisions.

Catalyst

• Catalysts provide an alternative reaction pathway with a lower activation energy, increasing the reaction rate without increasing collision frequency.
• Catalysts are not used up in the reaction, allowing them to be used again.