Chemistry Notes PDF

# Chemistry Notes ## 04-09-24 - Chemistry - **Chemistry** is the study of **matter**. - **Matter** is anything that has **mass** and occupies **space**. ### Matter - **Pure** - **atoms** - **elements** - **molecules** - **compounds** - **Impure** - **mixtures** ## Atoms & Th...

# Chemistry Notes ## 04-09-24 - Chemistry - **Chemistry** is the study of **matter**. - **Matter** is anything that has **mass** and occupies **space**. ### Matter - **Pure** - **atoms** - **elements** - **molecules** - **compounds** - **Impure** - **mixtures** ## Atoms & The Periodic Table - **Atom** - An atom is the smallest invisible particle of matter that can exist on its own. - **Element** - An element is a number of the Periodic Table that is made up of atoms of the same type. - Elements vary because their atoms consist of different numbers of **protons**, **neutrons**, and **electrons**. - **electrons** - electron shells - electrons (-ve) - **nucleus** (+ve - positively charged) - protons (+ve) - neutrons (neutral) ## 25/09/24 - Chemistry ### Electronic Configuration - The electronic configuration of an atom - Electrons are found in every level, or shell, or orbit to the nucleus. - The first shell is closest to the nucleus and is from the lowest energy level. - The further a shell is from the nucleus the higher the energy level. - Each shell can hold only a certain number of electrons. - The shell which is furthest away from the nucleus is called the outermost or **valence** shell. - The electrons which are in this shell are called **valence electrons** and are at a higher energy level than the shells closer to the nucleus. - **Rules for writing electronic configuration** - Electrons fill up energy levels closest to the nucleus first. - Each shell has a maximum number of electrons it can hold: | Shell no. | Maximum no. of electrons | |---|---| | 1 | 2 | | 2 | 8 | | 3 | 18 (Fill & first) | - When one shall is filled or has reached its maximum number, move on to another shell. - The outermost or valence shell can hold a minimum of 8 electrons. ## 18/09/24 - Chemistry ### Properties - The masses of subatomic particles are very small. - So since the nucleus contains protons and neutrons, most of the mass of the atom is centered in the nucleus - **Properties of Sub-Atomic Particles** | Sub-atomic particles | Relative Mass | Relative Charge | |---|---|---| | Protons | 1 | +1 | | Neutrons | 1 | 0 | | Electrons | 1/1840 or negligible | -1 | - Protons (+ve) and electrons (-ve) have opposite charges and neutrons have no charge. - The opposite charges of protons and electrons enable the atom to keep hold of its electrons due to the charges of opposite electrons. ## Notation of an Element - Each atom has an atomic number and a mass number which are displayed on the periodic table: The larger number is the mass number and the smaller number is the atomic number. - The atomic number tells us the number of protons which is unique for each element. - The number of electrons is equal to the number of protons. The atomic number also gives the number of electrons. - The atom has no overall charge since protons and neutrons in the nucleus. ### Calculating number of subatomic Particles - To calculate the number of subatomic particles in an atom, its atomic and mass numbers are used. - number of protons = atomic number - number of electrons = atomic number - mass number = number of protons + number of neutrons - number of neutrons = mass number - number of protons ## 02/10/24 - Chemistry ### Electronic Configuration | Element | Symbol | Number of Electrons | Electronic Configuration | |---|---|---|---| | Hydrogen | H | 1 | 1 | | Helium | He | 2 | 2 | | Lithium | Li | 3 | 2,1 | | Beryllium | Be | 4 | 2,2 | | Boron | B | 5 | 2,3 | | Carbon | C | 6 | 2,4 | | Nitrogen | N | 7 | 2,5 | | Oxygen | O | 8 | 2,6 | | Fluorine | F | 9 | 2,7 | | Neon | Ne | 10 | 2,8 | | Sodium | Na | 11 | 2,8,1 | | Magnesium | Mg | 12 | 2,8,2 | | Aluminium | Al | 13 | 2,8,3 | | Silicon | Si | 14 | 2,8,4 | | Phosphorus | P | 15 | 2,8,5 | | Sulfur | S | 16 | 2,8,6 | | Chlorine | Cl | 17 | 2,8,7 | | Argon | Ar | 18 | 2,8,8 | | Potassium | K | 19 | 2,8,8,1 | | Calcium | Ca | 20 | 2,8,8,2 | ## 06/11/24 - Chemistry ### Chemical Bonding **Atom** - **Elements** - Substances which consist as only one type of atom - **Metals** - Metallic bonds - **Compounds** - Consist of atoms of different elements - **Ionic** - Metal & non-metal bonds - non-metals - Covalent bonds - **Covalent** ## How and why do elements bond? - Consider: - Helium (He) - 2P, 2n - Neon (Ne) - 10p, 10n - Argon (Ar) - 18p, 22n - Helium, Neon and Argon are in group 8 and zero (0), which is the last group of the periodic table. - They are called Noble and Inert Gases. Atoms of these elements are stable and unreactive in nature as individual atoms because they have full outer electron shells or a stable octet. - Atoms of most other elements are not stable because they do not have full valence shells. - These atoms become stable by bonding which either occurs with the same atom or different atoms to form compounds. ### They can do this by: - Losing valence electrons - **metal** atoms with 1, 2, or 3 valence electrons (electrons of the valence or outermost shell) lose these electrons. - Gaining valence electrons - **non-metal** atoms with 5, 6, or 7 valence electrons can gain electrons from metal atoms. - Sharing valence electrons - non-metals with 4, 5, 6 or 7 valence electrons in their valence shells, share these electrons with other non-metal atoms. - NB: Only electrons of the valence shells are involved in bonding. ## 10/09/24 - Chemistry ### Isotopes | Protons | Neutrons | Electrons | | |---|---|---|---| | 6 | 6 | 6 | Carbon-12 (12C) | | 6 | 7 | 6 | Carbon-13 (13C) | | 6 | 8 | 6 | Carbon-14 (14C) | - You can identify atoms of an element by its atomic number or the number of protons in an atom. All Carbon atoms have 6 protons but not all Carbon atoms are identical: Some have more neutrons than others. - **Isotopes** are different atoms of a single element that has the same number of protons but different numbers of neutrons. - Therefore isotopes of an element have the same atomic number but a different mass number. - Isotopes of an element have the same chemical properties because the number or arrangement of electrons is almost the same. - They have slightly different physical properties - most atoms have the same physical properties but because they have slightly different masses - most elements have isotopes. ## 10/16/24 - Chemistry ### Radioactive Isotopes - Carbon-14 atom behaves in a strange way. It is radioactive. That means it naturally or decays unstable and can break down into more stable giving out radiation to become more stable. - Like Carbon, several other elements have radioactive isotopes that occur naturally but eventually decay. ### Uses of radioactive isotopes: 1. Carbon-14 dating - the age of a plant or animal remains (fossils) can be determined by Carbon-14 dating. 2. Cancer treatment - radioactive isotopes can be directed to tumors such as Cobalt used for destroying cancer cells. 3. Traces - Very small quantities of radioactive isotopes such as Carbon-14 is used in medical and biological research.