Introduction to Elements & the Periodic Table

1. Introduction to Elements & the Periodic Table

2. Introduction to Atoms • The first known culture to think about the nature of matter were the Greeks. • Around 430 B.C., a Greek philosopher named Democritus proposed the idea that matter was formed from smaller pieces called “atomos” or “uncuttable”. • Unfortunately, Democritus was unable to prove this idea. • Later, philosophers like Aristotle would advocate the idea that all matter was made up of a combination of only four elements: Fire, Water, Earth, & Air. • It was this false idea that would be taught until modern times.

3. Early Chemistry: Alchemy • During the Middle Ages, there were several people that practiced that art of Alchemy. • Alchemy - • Alchemist were often treated more as magicians than scientists. • Many believed it was possible to turn lead (Pb) into gold (Au) • Some believed it was possible to create an elixir that could stop aging or grant immortality • Even though alchemist didn’t always practice good science, they did make several scientific discoveries. • They discovered the elements mercury, sulfur, and antimony • They discovered several properties of common elements • They learned how to prepare acids • They learned how to create alloys • They developed new glassware for experimentation

4. Development of the Atomic Model • In modern times, scientists returned to the idea that matter was made up of smaller units called atoms, but they still couldn’t describe what atoms looked like. • Several scientists from the 1600s to the 1900s proposed different models to explain how atoms behaved and what they looked like. Dalton’s Model Thomson’s Model Rutherford’s Model Bohr’s Model

5. Modern Atomic Model • In the 1930s the current atomic model was designed. • Atoms are composed of a tiny nucleus at the center of the atom that contain protons and neutrons. • The nucleus is surrounded by an electron cloud that contains electrons. These electrons occupy certain areas of the electron cloud, but are in constant, random movement.

6. Atomic Particles • Even though atoms are considered the smallest form of matter, they are actually composed of smaller particles; each with unique properties that give the element its characteristics. • An element’s overall characteristics are determined by the number of atomic particles found in each atom. • Protons & Neutrons make up the majority of the mass in each atom. Electrons also have mass, but are generally not considered in when calculating the total mass of each atom.

7. Atomic Number & Mass • Every element has a specific atomic number that is unique to that element. • Atomic Number – The number of protons in the nucleus of an atom. • Examples: • Hydrogen always has an atomic number of 1 • Carbon always has an atomic number of 6 • Uranium always has an atomic number of 92 • Although all atoms of an element have the same number of protons, their number of neutrons can vary. • Atoms with the same number of protons, but a different number of neutrons are called isotopes. • Isotope – Atoms with the same atomic number, but different atomic masses. • Atomic Mass - The total number of protons and neutrons in the nucleus of an atom. • Examples: • Carbon has three common isotopes: • Carbon-12, Carbon-13, & Carbon-14 • Carbon-12 has 6 protons and 6 neutrons (Atomic Number 6, Atomic Mass 12) • Carbon-13 has 6 protons and 7 neutrons (Atomic Number 6, Atomic Mass 13) • Carbon-14 has 6 protons and 8 neutrons (Atomic Number 6, Atomic Mass 14)

8. Reading Elemental Squares • To help scientists study elemental information, their atomic number, mass, symbol, and name are listed on Elemental Squares. • Atomic/Chemical/Elemental Symbol – The universally accepted abbreviation of the element’s name. • Abbreviations can be 1-2 letters, only the first letter is ever capitalized to avoid confusion. (Hypothetical elements yet to be created have three letter abbreviations until they are “discovered”.) • Most chemical symbols are abbreviated from the element’s name in English, but some are also Latin. • Examples: • Iron, or Ferrum in Latin, has the chemical symbol: Fe • Lead, or Plumbum in Latin, has the chemical symbol: Pb • Note that the Atomic Mass/Weight sometimes is not a nice whole number. That number represents the calculated average of all of that element’s isotopes found in nature.

9. Organizing the Elements • The Periodic Table get its arrangement from a Russian scientist name Dmitri Mendeleev in 1869. • At the time, scientists had discovered the atomic mass and reactive properties of several elements, but not their atomic numbers. (There were also only 63 known elements at the time!) • Mendeleev decided to organize the known elements in a table by their common properties and in order of increasing atomic mass. (Legend says that this idea came to him in a dream after he had been working for several weeks in vain on organizing the elements.) • In arranging the elements by common properties, Mendeleev noticed that there were gaps in his table. He predicted that these would be filled by yet-to-be-discovered elements. • Over the next 16 years, scientists discovered these missing elements. This helped to prove that Mendeleev’s system of organization was correct.

10. Modern Periodic Table • As the years passed, new elements were added to the periodic table as they were discovered and arranged by property and atomic mass. • In 1913, a British scientist named Henry Moseley discovered how to calculate the positive charge of atoms. This became known as the atomic number of atoms. • This discovery altered Mendeleev’s periodic table slightly, but not enough to create a new table. • Today, elements are arranged on the periodic table according to atomic number and chemical properties.

11. The Periodic Table • The modern periodic table organizes the elements by atomic number and similar chemical properties according to Group & Period. • Groups are the vertical columns of the periodic table. • Groups can also be called Families. • All the elements in a group have similar chemical properties that are often related to their valence electron shell. • For example: All the elements in Group 1 have only one electron in their outermost electron shell. • Periods are the horizontal rows of the periodic table. • From left to right, the properties of the elements change in a pattern: elements on the left side of the table are highly reactive metals, less reactive metals are in the middle, then the metalloids, followed by the nonmetals & noble gasses on the right.

12. Characteristics of the Periodic Table • The periodic table can be divided into three main groups: Metals, Nonmetals, & the Noble Gases. • Metals are shiny, malleable, ductile, conductive. • Nonmetals are dull, brittle, and poor conductors of electricity & heat. • Noble gases are generally unreactive with anything. • There are also two odd areas of the periodic table: • Metalloids – Elements on the border between metals and nonmetals that exhibit characteristics of both groups. • Hydrogen – Hydrogen is the most abundant element in the universe. It is a nonmetal, but reacts in the same way as alkali metals. Even so, it is considered in a class all its own.

13. Metal Groups • The elements in column 1 are called the Alkali Metals. • These elements react with other elements by losing one electron. • They are so reactive, they are always found combined with another element in nature. • The most important alkali metals are Sodium (Na) and Potassium (K). • The elements in column 2 are called the Alkaline Earth Metals. • These elements react by losing two electrons. • While less reactive than the alkali metals, they are more reactive than most other metals. • Most common alkaline earth metals are Magnesium (Mg) and Calcium (Ca). • Elements in groups 3-12 are called the Transition Metals. • Transition metals are good conductors of electricity and don’t react well with other elements.

14. Odd Metal Groups • Mixed Metal Groups • There are some metals in groups 13-16; mixed in with the nonmetal groups. • These elements are not very reactive with each other. • The most familiar mixed metals in these groups are aluminum and lead. • Lanthanides & Actinides • Also known as the “Rare Earth Elements”. • Theses elements have similar properties to the elements in Group 3 so to make the periodic table easier to read, they are placed in a separate row at the bottom. • Many of these metals are used in technology to make alloys. • Uranium is the largest element found in nature.

15. Nonmetal Groups • There are four groups of elements that make up the nonmetals: • The Carbon Family – Elements in this family can gain, lose, or share four electrons. This gives them exceptional bonding abilities with other elements. Carbon (C) is the most essential element for life and is found in all living things. (Organic Compounds) • The Nitrogen Family – Nonmetals in this family include Nitrogen (N) and Phosphorus (P). Nitrogen is the most abundant element in the atmosphere and occurs as a diatomic molecule. • The Oxygen Family – Elements in this family usually gain or share two electrons when they bond with other elements. They are often very reactive, which explains why Oxygen (O) is the most abundant element in the Earth’s crust and the second most abundant element in the atmosphere. Oxygen is also used to create water (H20) • The Halogen Family – These elements are the most reactive of the nonmetals because they will steal or share an electron from another element. Elements in this family often form salts by combining with an alkali metal. (ex: Sodium Chloride (NaCl)) Even though halogens are dangerous in their pure form, they can be very useful in when they combine with other elements.

16. Noble Gases & Metalloids • Noble Gases are elements that don’t react with other elements due to having a full valence electron shell. (Most elements want a full shell of 8 electrons) • Metalloids consist of a group of seven elements that form the border between the metals and nonmetals. All are hard, brittle, somewhat reactive with other elements. • Metalloids are known for their varying ability to conduct electricity. This makes them great semiconductors. • Semiconductor – A substance that can conduct electricity under some conditions, but not under other conditions. • Silicon (Si) is the most common metalloid and is used in a lot of computer components.

17. Where do elements come from? • There are only 118 different forms of known physical matter in the universe. • Where did all this matter come from? • The Big Bang Theory states that all matter was created in a single instantaneous event, which exploded outward from a single point of origin. • The matter created from this event started as pure energy and later condensed into solid matter in the form of Hydrogen (H). • From this point, all heavier matter formed from nuclear fusion.

18. Nuclear Fusion • As gravity draws matter together, their combined thermal energy increases. • As the temperature increases, the matter turns into plasma forming stars. • In the center of stars, the heat and pressure becomes so great, that atoms smash together to form new elements. This is called nuclear fusion. • During nuclear fusion, heavier elements form along with energy & light. • The bigger the stars, the heavier the elements can form. • A star the size of the Sun has enough energy to form elements up to the element Oxygen (O). • Bigger stars can form elements up to the element Iron (Fe)

19. Supernovas • Elements heavier than Iron (Fe) can only form during Supernova events. • Supernovas occur when a star explodes. • This event causes the heat and pressure inside a star to dramatically increase, causing heavier elements to form. • Elements up to Uranium (U) have been known to form during these events. • Elements heavier than Uranium have only been known to be created synthetically from particle accelerators. • Particle accelerators are machines that move atomic nuclei so fast that they can sometimes form heavier elements when they are smashed together. • These form what are known as Synthetic Elements.

20. Radioactive Elements • Earlier in the unit, we discussed how alchemist thought that you could turn one element into another. • While they failed, it is possible for some elements to turn into other elements through a process called radioactive decay. • Radioactive Decay – When the atomic nuclei of unstable isotopes release fast moving particles & energy.

21. History of Radioactive Discovery • In 1896, a French scientist named Henri Becquerel first discovered radioactivity in Uranium (U). • He shared his discovery with a married couple named Pierre & Marie Currie. They were able to correctly deduce that the radioactivity was coming from the unstable atomic nuclei of the element. • Pierre & Marie Currie both won a Nobel Prize for this work. (The first married couple to do so.) • Marie Currie continued to work with radioactive elements and discovered two more named Polonium (Po) and Radium (Ra). • She won a second Nobel Prize for this and became the first female scientist to win a Nobel Prize for Science.

22. Types of Radiation • There are three different types of radiation: • Alpha Particles • Beta Particles • Gamma Radiation • Each type of radiation moves at different speeds with different levels of energy. • Depending on the type of radiation, they can cause a number of different effects; some dangerous. • Radiation does have some positive benefits and can be used in medicine and as tracers.