Chemistry 10th Class: Matter and Atomic Structure

SI System Units

• Length: meter
• Time: second
• Amount of substance: mole (mol)
• Electric current: ampere (amp)
• Temperature: Kelvin
• Mass: kilogram

Matter

• Matter is a physical substance with mass and occupies space.

Atomic Structure

• Atomic number: number of protons in an atom's nucleus
• The number of protons equals the number of electrons in a neutral atom.
• Atoms with the same number of protons are the same element.
• Atomic mass: sum of protons and neutrons in an atom.
• To find the number of neutrons, subtract the number of protons from the atomic mass.

Isotopes

• Isotopes are different versions of the same element.
• Isotopes have the same number of protons but a different number of neutrons.
• Isotope number: total number of protons and neutrons.
• Average atomic mass calculation: weighted average of the masses of different isotopes based on their natural abundance in percentage.

Conservation of Mass

• Matter cannot be created or destroyed in a chemical reaction.
• All atoms present in the reactants are present in the products, in some form.
• Small mass loss in chemical reactions is due to released energy.

Balancing Equations

• In chemical equations, balance the atoms on both sides of the equation to maintain conservation of mass.
• Balance the oxygen atoms first and then balance the other elements.

Limiting and Excess Reagents

• Limiting reagent determines the maximum amount of product. (Complete and balance the chemical equation, convert to moles)
• Use the mole ratio to calculate the moles of the product from the limiting reagent.
• Find the mass of the product.

Stoichiometry

• Mole to mole conversions: Use coefficients in balanced equations.
• Mole to mass conversions: Calculate product mass using molar mass.

Percent Yield

• Percent yield: actual yield/theoretical yield x 100%.
• Actual yield: experimentally obtained amount of product.
• Theoretical yield: maximum amount of product calculated.

Chemical Bonding

• Ionic compounds: solid at room temperature, formed between metals and nonmetals.
• Covalent compounds: formed between nonmetals, can be in any state (solid, liquid, gas).

Molecular Shapes

• Molecular shapes and bond angles are important aspects of covalent compounds. (Shape list given in the document)

Electronegativity/ Atomic Radius

• Electronegativity increases across a period and decreases down a group.
• Atomic Radius increases down a group and decreases across a period.

Ionic Radius and Ionization Energy

• Ionic radius of a cation is less than atomic radius.
• Ionic radius of an anion is greater than atomic radius.
• Ionization energy is the energy needed to remove an electron from a gaseous atom.

Electron Affinity

• Electron affinity is the energy released when an electron is added to a gaseous atom.

Gas Laws

• Charles' Law: volume varies directly with temperature at a constant pressure.
• Boyle's Law: pressure varies inversely with volume at a constant temperature.

Standard Temperature and Pressure (STP)

• Universal value of STP: 1 atm pressure and 0°C (convert to Kelvin).
• 1 mole of gas occupies 22.4 L at STP..
• Use Ideal Gas equation when amount of gas and mass are given.

Lewis Structures

• Lewis structures are used to represent molecules and polyatomic ions.
• Valence electron count.
• Determine number of bonds needed to complete the octet rule.
• Central atom.
• Skeletal structure.
• Place electrons outside the atoms.