Updated Chemistry Notes Topic C PDF

Chemistry Topic C Content Advances in our Understanding of Chemistry Chemistry Topic C Table of Contents Topic C 1: How observations have advanced our understanding Topic C 2: The Periodic Table Topic C 3: Ionic and Molecular compounds Topic C Review Topic C Vocabulary Topic C...

Chemistry Topic C Content Advances in our Understanding of Chemistry Chemistry Topic C Table of Contents Topic C 1: How observations have advanced our understanding Topic C 2: The Periodic Table Topic C 3: Ionic and Molecular compounds Topic C Review Topic C Vocabulary Topic C 1: How observations have advanced our understanding (Textbook pages 114-134) Democritus :(Greek) said matter was made of particles based on his observations of how substances interact. He was right but Aristotle said matter was made of air/earth/water/fire and everyone believed him. Alchemists believed Democritus (rightly so) and used his ideas to try and find ways to create gold from other elements. They didn’t, but discovered plaster of Paris and created several useful types of lab equipment. Topic C 1: How observations have advanced our understanding (Textbook pages 114-134) Observations about electrical principles led to many discoveries in chemistry. For example, by experimenting with adding electricity to water it was discovered that the water molecule could be broken down into simpler components (elements of hydrogen and oxygen) that behaved very differently than water. Other elements were also discovered when electricity was added. Study of the electrical conductivity of acids and bases led to the realization that when they chemically reacted, new molecular substances were formed that were different than the original ones. This explained why the new products had different Development of the atomic model John Dalton (early 1800s): proved the existence of atoms. He observed that different substances behaved differently and proposed that this was because matter was made of different types of particles. He believed these were solid spheres with different mass and size – something like billiard balls. J.J. Thomson discovered the electron. He found that rays were given off when an electric current was passed through a gas at low pressure. The rays were particles with a negative charge. Since these rays were given off by atoms, which were known to be neutral, Thomson proposed that the atom consisted of thousands of negatively-charged electrons embedded in a massless positive-charged sphere. Ernest Rutherford (early 1900s): discovered the nucleus. He carried out a series of experiments while working at McGill University in Canada where he fired a beam of alpha particles at a thin sheet of gold foil. Alpha particles are actually helium nuclei and are positively charged since there are no electrons. When they were shot at the gold foil, most went right through, missing the gold nucleus completely. However, some were deflected at an angle, or came straight back. This proved that the positive helium nucleus was being repelled by the positive gold nucleus. This led Rutherford to correctly infer the presence of a small, highly concentrated part of an atom (the nucleus) within a larger, negatively charged area (the electrons). Rutherford then proposed that the nucleus was orbited by electrons, in the same way that Rutherford’s experimental planets orbit the Sun so his model of the atom setup is called the planetary model. Niels Bohr discovered that electrons exist at certain levels since he needed to answer the question of why the negative electrons don't just crash into the positive nucleus. He proposed a model where electrons each occupy separate energy levels called the Bohr Model. Valence (outermost) electrons became very important. Although dated, this model is still useful to explain chemical behavior. James Chadwick discovered that there were both neutrons and protons in the nucleus, and also discovered isotopes. Quantum model predicts that electrons move so quickly around the nucleus of an atom that it essentially acts like a negatively charged cloud. Physicists use the quantum model to explain particle behavior and it is the most up-to-date model we Summary of atomic theory: We can thank Einstein for mathematically proving that atoms actually do exist! The Bohr Atomic Model Subatomic particles (protons, neutrons, electrons) make up the atom. The strongest force in the universe - nuclear force - holds the atom together. Nucleus – contains positively charged protons and neutral neutrons. Eureka what is an atom 5 min Eureka atoms and electrons 5 min The Bohr Atomic Model These subatomic particles each have a mass of one amu (atomic mass unit which is very little). Protons positively charged, reside in the nucleus Neutrons help space out protons so that their positive charges don’t just force them to separate. Negatively charged electrons orbit the nucleus. The mass of this subatomic particle is so small that it is treated as zero. Valence electrons This diagram shows a sodium atom. The electrons on the outermost shell are called valence electrons and you will be learning about their importance in chemical reactions as we move on. They control how reactive or unreactive an element will be. The inner ring of all atoms can only hold a maximum of two electrons. Other rings can hold more. Topic C-2: The Periodic Table (Page 120-134) Elements are pure substances made up of only one kind of atom. They cannot be broken down into smaller particles. Scientists wanted to classify and organize elements for common reference. The first elements were represented by symbols, and later by letters. When scientists were able to determine atomic mass (weight of a single atom), elements were grouped from smallest mass to greatest mass in the periodic table. Topic C 2: The Periodic Table (Page 120-134) Dmitri Mendeleev observed that when ordered by mass, certain groups of elements had similar physical and chemical properties. He arranged them like a solitaire game, in rows and columns. Where there were gaps in his “game board”, Mendeleev correctly predicted that they would be filled by future discoveries. Periodic Table boxes Each box on the periodic table contains information about one particular element. All have at least the symbol and the atomic number. They may or may not have the name, atomic mass and ionic charge.  ○ Atomic number shows how many protons are in the nucleus of an atom of the element. ○ In a stable element, the number of protons, neutrons and electrons are the same. ○Atomic mass is the total mass of all the protons and neutrons in an atom of the element. This number is usually about double the atomic number but not always. Isotopes have the same number of protons but different numbers of neutrons. The atomic mass number that you see on the periodic table is an average for all of the naturally occurring isotopes for an element. That means that some atoms will have fewer neutrons and some will have more. You can figure out the number of neutrons by subtracting the number of protons (atomic #) from the mass. The symbol represents the short form of the element name. If there are two letters, the second letter is always lower case. A stable lithium atom would look like this: A lithium atom has atomic number 3 so there are three positive protons in the nucleus. It is a stable atom so there are three negative electrons to balance the three protons. The atomic mass is 6 so there are three neutrons (protons + neutrons = atomic mass). However, atoms are not always stable! Ions have unequal numbers of protons and electrons so they have an electrical charge. In the examples below, ++ represents protons and -- represents electrons. +++ and --- would represent a stable atom where protons and electrons are balanced. +++ and -- would represent an ion with a 1+ ionic charge since there is one missing electron. +++ and ---- would represent an ion with a 1- ionic charge since there is one extra electron. Isotopes: Isotopes are atoms with unequal numbers of neutrons and protons. They are sometimes radioactive. This isotope of lithium has three protons but four neutrons. Therefore, its atomic mass is going to be 7. Below are three different isotopes of lithium. Scishow Nucleus Periodic Table patterns Horizontal rows are called periods (think of them as ending in a period like a sentence). Periods tell you the number of orbital shells an atom has. Vertical columns are called groups or families. Each group (all elements falling within that column) have similar properties and behave with other materials in similar ways. The number at the top of the column tells how many electrons are in the outer orbital shell. These are called valence electrons. ○ Everything in group 1 has one electron on its outer shell. This makes it very reactive since it easily loses this electron. Therefore, every element is group 1 is a very reactive metal. They are called the alkali metals and can be very explosive. Scishow Periodic Table Vertical columns are called groups or families. Every element in group 7 (17 on some tables) has 7 valence electrons. They gain an extra electron quite easily and this makes them very reactive non-metals (they are called halogens and can be very corrosive). Elements become less reactive toward the center of the table. The exception is elements in group 8 which are noble gases. These behave similarly to each other, in that they are not reactive at all. Scishow Periodic Table  Predicting reactivity based on periodic table position You can predict how reactive one element is relative to another by looking at its location on the periodic table. This is because reactivity depends on valence electrons – the number of electrons on the outermost shell. Elements in group 1 have 1 valence electron. Elements in group 2 have 2, etc. Notice that metals have fewer valence electrons (1-5) than nonmetals (4-8). Why is there a difference in reactivity? All elements want to have a stable outer shell which consists of 8 valence electrons (with the exception of helium since it only has one shell and that small shell only has room for 2 electrons, making it stable with 2). Metals reach stability by losing their outer electrons during a chemical reaction with another element. The fewer outer electrons, the easier it is to lose them. Therefore, all elements in group 1, with only one valence electron, are extremely likely to react. They are extremely reactive. Because non-metals have more valence electrons than metals, it is easier for them to gain enough electrons to fill their outer shell during a chemical reaction. This is especially true of elements in group 7 since they only need to gain one. This makes them extremely reactive. Because elements in group 8 are stable already, they are unreactive. They have a special name – noble gasses. IMPORTANT CONCEPT: Elements in the same group (column) have the same number of valence electrons so have similar reactivity.  This diagram should help you visualize the reason for periods (number of electron shells) and groups or families (number of valence electrons on the outer shell). You can also see how the number of valence electrons directly affects the reactivity of elements. The group 1 metals and group 7 nonmetals are the most reactive because they have the fewest electrons to move in order to become stable. Reactions of alkali metals 2 ½ min Reactions with halogens 1 min Why you don’t use francium in washer 30 sec This is just an interesting version of the periodic table showing relative abundance of the different elements. You don’t actually need to know this. Topic C-3: Ionic and Molecular Compounds (page 144-153) Ionic Compounds Nature will always choose to be balanced and low energy. For an atom, that means it has 8 electrons on its outer shell. Hydrogen and helium are exceptions since they are tiny atoms and their single shell will only hold two electrons. When an atom gains or loses one or more electrons so that the positive protons and negative electrons are no longer balanced, it becomes in ion. Only the outer valence electrons are involved in this loss or gain. The ionic charge identifies the type of ion. For example, sodium is in group 1 because it loses its outer valence electron, resulting in an overall 1+ ionic charge. Fluorine is in group 7 and easily gains one valence electron so its ionic charge is 1-. Metals all have positive ionic charges since it is easier for them to give up a few electrons to become stable. Non-metals have negative ionic charges since it is easier for them to gain electrons to become stable.  In this diagram, sodium has one outer valence election and chlorine has seven. If they come into contact, they will chemically react. Sodium will give up its one electron to achieve 8 valence electrons. It is now an ion with a 1+ ionic charge. Chlorine accepts the electron and now also has 8 valence electrons and is an ion with a 1- ionic charge. Opposites attract. The atoms form an ionic bond and are now stable and happy as a sodium chloride molecule. Sodium chloride (or table salt) is a common ionic compound made from a metal and a nonmetal. All ionic compounds are made from a Explanation of ionic bond 6 min metal and a nonmetal. Formation of ionic compounds 2 min Molecular Compounds Molecular compounds are made of non-metals. Molecular compounds are held together with covalent bonds which share electrons between atoms. As with ionic compounds, the atoms want to obtain low energy outer shells with eight electrons (or two in the case of hydrogen since that is a full shell). However, there are no oppositely charged ions this time. Instead, atoms will share electrons with one another in order to reach stability. In this illustration, the hydrogen atom only has one electron on its outer shell and it needs two to be stable. Oxygen has six valence electrons so needs to more. By reacting with two hydrogen atoms and sharing the electrons, both hydrogen and oxygen form a stable water molecule. What a covalent bond would look like 30 sec Molecular bonds explained 6 min Properties of Ionic and Molecular Compounds Because ionic compounds consist of at least one metal (+ ion) and one non-metal (- ion), they tend to have properties similar to the metal elements on the periodic table in most, but not all ways since they do include a non-metal. The properties of molecular compounds are most like non-metals. Type of Types of Type of State Meltin Conductivi Streng Crystal Compoun Elements bonding at g and ty th shape d room Boilin temp g Point Ionic Metal + Ionic – Solid High Will Strong Often Non-metal attraction of conduct distinctive + metal ion when (ex. to dissolved in Cubic) – non-metal solution ion Molecular Non- Covalent – Solid, Low Will not Weak No metals atoms share liquid conduct distinct outer or gas shape valence electrons Ionic solution: the ions are now free to move about and conduct electricity so the ionic solution can be a conductor even though the solid compound cannot.  Matter and Chemical Change Topic C Topic C-1: Democritus andTopic Review alchemists; Concepts Dalton billiard ball model; and Vocabulary Thompson raisin bun model; Rutherford’s atomic model and experiment; Chadwick’s atomic model; Bohr atomic model; Quantum atomic model; Atom and subatomic particles; Relationship between density and mass of nucleus; Valence electron Slides 3-9 Topic C-2: Dmitri Mendeleev; Components of an element box in the periodic table; Ion; Isotope; Relate ionic charge to number of protons and electrons; Periods in the periodic table; Groups or families in the periodic table; Metals, metalloids and non-mentals in first 18 elements; Stable outer shell or orbit; Role of valence electrons in reactivity of elements; Reactivity of different groups in the periodic table; Noble gas Slides 10-21 Topic C-3: Ionic compounds; Ionic bond; Molecular compounds; Covalent bond; Compare characteristics of ionic and molecular compounds; Ionic solution Slides 22-26 You MUST know the first 18 elements on the periodic table and be familiar with  Chemistry Topic C Vocabulary 1. Dmitri Mendeleev recognized a pattern similar to a solitaire game and ordered the elements in rows and columns. This classification of elements became known as the periodic table. 2. An element is a pure substance with characteristics that make it different from every other element. 3. Democritus was a Greek philosopher, and the first person to suggest that matter was made up of tiny, invisible particles that we now know as atoms. 3. Alchemists were trying to discover how to make gold but came up with many tools that furthered the study of real chemistry at a later date. 4. John Dalton inferred that atoms must be like billiard balls with charged particles embedded in them. 5. J.J. Thompson was the first scientist to come up with the idea of subatomic particles and he created the “raisin bun” atomic model. 6. Ernest Rutherford discovered that certain subatomic particles were too massive to pass through a gold screen that would allow electrons through, and inferred that there must be a dense nucleus in atoms. 7. Rutherford’s model, with the nucleus in the middle and electrons orbiting around it, became known as the planetary model of the atom. 8. James Chadwich focused his work on the nucleus and discovered that there were two different kinds of particles there – protons and neutrons. 9. Niels Bohr discovered an atomic model with electrons in energy levels (orbital shells) around the nucleus. 10. The model still used by chemists was discovered by Bohr, and is called the Bohr model. It introduced the idea of energy levels in atoms. 11. The most recent atomic model is called the quantum model and has given rise to the science of quantum physics. 12. The atom is the smallest part of an element that still has all of the properties of that element. 13. Atoms are made of even smaller parts called subatomic particles. These include protons, neutrons and electrons. 14. The nucleus of an atom is at the centre and contains both protons and neutrons. The nucleus makes up the mass of the atom. 15. Protons are positively charged subatomic particles in the nucleus of an atom. 16. Neutrons and neutral (no charge) subatomic particles in the nucleus of an atom. 17. Electrons are negatively charged subatomic particles that orbit around the nucleus of an atom. 18. The mass of an atom determines the density of an element made from that atom. Materials with greater atomic mass form substances that are more dense. 19. The atomic number tells how many protons are in the nucleus. 20. The total mass of all protons and neutrons in the nucleus is the atomic mass (measured in amus or atomic mass units). 21. Each box on the Periodic Table represents one unique element. The element symbol is the letter that represents that element for chemists. 22. An atom that has one too many electrons is called a negative ion because it has an overall negative ionic charge. A 23. An ion is an atom with an unbalanced electrical charge – either too few or too positive ion has too few electrons. many electrons to balance the positive protons in the nucleus. 24. The number of protons in in an atom of an element never change. The number of neutrons can, and isotopes are atoms with of a specific element with different numbers of neurons. 25. Horizontal rows on the periodic table represent the number of shells for electrons on an atom. All atoms in these periods have the same number of shells and rings. 26. Vertical columns are called groups or families and all elements in a column have the same number of electrons in their outer shell. Because of this, their chemical behavior is very similar. 27. Valence electrons are on the outermost ring and control how reactive a particular element will be. 28. Ionic compounds are the result of a chemical reaction between a metal and a non-metal. 29. Ionic bonds are the result of opposite electrical charges attracting. The metals lose and electron and the non-metals gain one. 30. Molecular compounds are the result of a chemical reaction between two non- metals. 31. Molecular compounds are held by a covalent bond in which valence electrons are shared between atoms of two Non-metals.