Understanding the Periodic Table

The Periodic Table

• Dmitri Mendeleev arranged the first 63 known elements by their properties and compositions.
• Mendeleev left spaces in the table, anticipating new elements would be discovered to fill them.
• The horizontal rows on the periodic table are called periods.
• The vertical rows on the periodic table are called families or groups.
• Families/groups share similar properties.
• Each element on the periodic table includes an atomic symbol and numbers that give information about it.
• The atomic number tells how many protons are in one atom of that element.
• The atomic number also tells how many electrons are in each neutral atom because the number of protons (+) and electrons (-) is equal.
• Atomic mass is the total number of protons and neutrons in an atom.
• To calculate the number of neutrons, subtract the number of protons from the atomic mass.
• Ionic charge shows how many electrons an atom will lose or gain in a chemical reaction.
• An element with a negative ionic charge has gained electrons i.e., Fluorine which has gained an electron (-) so it now has an extra negative charge.
• An element with a positive ionic charge has lost electrons i.e., Sodium which has lost one electron, so it now has a positive charge of 1.

Periodic Patterns

• The periodic table contains patterns related to element properties.
• Green elements are metals which are, shiny, malleable, and conduct electricity
• Orange elements are non-metals which are dull, brittle, do not conduct electricity (except carbon), and are called insulators. non-metals can be solids, or gases.
• Purple elements are metalloids which share a mix of metal and non-metal properties.
• Groups and families are numbered 1-18.
• Groups/families are usually called by the first element in their column; Group 5 is the Vanadium family.
• Group 1 elements are Alkali Metals, which are highly reactive and react with exposure to oxygen or water.
• Group 2 elements are Alkali Earth Metals, which are not as reactive as Alkali Metals.
• Group 17 elements are Halogens which are very reactive non-metal elements.
• Group 18 elements are Noble Gasses which are the most stable and unreactive elements.

Matter and Chemical Change

• Pure substances contain only one type of particle.
  • Elements on the periodic table like gold, carbon, and oxygen are pure elements.
  • Compounds whose molecules all look the same (H20, CO2, etc.) are pure compounds.
• Substances that are not pure are mixtures.
  • Mechanical mixtures have visibly different components and are also known as heterogeneous mixtures.
  • Solutions appear like one substance but are made of different particles and are also known as homogeneous mixtures.
• Suspensions are cloudy mixtures where tiny particles of one substance are suspended within another and separate over time such as, tomato juice.
• Colloids are similar to suspensions, but they do not separate easily i.e, Milk
• Matter can be classified as one of three states: solid, liquid, or gas.
• To change the state of a substance, energy must be either added or removed.
• All types of matter have their own properties.
  • Physical properties describe the appearance and structure of the substance. Melting point, hardness, ductility, solubility, conductivity, lustre, boiling point, malleability, crystal shape, density, and colour are among the properties used to describe matter.
  • Chemical properties describe how substances interact with other substances.

Observing Change in Matter

• A physical change is a change in the state of matter that does not alter the particles of the substance.
• A chemical change occurs when two or more materials react and create a new substance with different properties from the original substance.
• These are examples of physical changes: Aluminum foil is cut in half, Clay is molded into a new shape, Butter melts on warm toast, Water evaporates from the surface of the ocean, A juice box in the freezer freezes , and Rubbing alcohol evaporates on your hand.
• These are examples of chemical changes: Milk goes sour, Jewelry tarnishes, Bread becomes toast, Rust forms on a nail left outside, Gasoline is ignited, Hydrogen peroxide bubbles in a cut, Food scraps are turned into compost in a compost pile, A match is lit, You take an antacid to settle your stomach , Your body digests food, and You fry an egg. The primary examples of chemical change are a change in color ,the formation of a new solid or gas, change in odor and the release or absorption of heat.
• Freeze-drying removes up to 90% of the moisture in food meaning it can be kept for much longer and all to do is add water.
• Scientists can take a common material like corn and create multiple things from it, like pop bottles, nail polish remover, and fuel for cars.
• When corn is fermented, it undergoes a chemical change, resulting in more uses, and corn products are then mostly biodegradable.

Evolution of Matter

• Science involves constantly re-evaluating our beliefs based on observation, which means theories change over time.
• Roughly 10,000 years ago, the first chemists lived.
• Metals hadn't been discovered yet, so chemists only had stone tools.
• Early chemists learned that they could manipulate or create substances once they discovered fire.
• The earliest chemists cooked, fire-hardened, and toughened materials.
• Around 7000 years ago, people discovered metals, which instantly became highly valuable.
• Gold was shiny and didn't tarnish.
• Copper was used for pots, coins, and tools and became one of the elements in bronze.
• Around 1200 B.C., hittites discovered how to get iron from rocks marking the start of the Iron Age.
• Combining Iron and Carbon creates steel.
• Cultures also started mummifying bodies using resin from plants.
• Roughly 2500 years ago, people realized that rocks could be broken into very small pieces.
• Democritus proposed that the smallest particle was called "atomos," which is Greek for "indivisible".
• Each material was made of its own “atomos.”
• For 2000 years after Democritus' theory, people practiced alchemy.
  • Alchemy was part magic and part science but is now considered a pseudoscience. - Alchemists believed that it was possible to turn anything into gold.
    • Alchemists performed some of the first chemistry experiments.
• Since Alchemy never succeeded, people looked deeper into the nature of matter.
  • Robert Boyle experimented with gases and developed Boyle's Law.
  • Boyle agreed that all matter was made of tiny particles.
• In the 1770s, Antoine Laurent Lavoisier studied chemical interactions and developed universal names for substances!
• Lavoisier's system named Hydrogen, Oxygen, and Carbon.
  • This allowed scientists in different countries to share ideas in a universal language!
• John Dalton decided that all matter was made of elements.
  • Elements are pure substances that cannot be divided into different substances.
• Atoms of the same element are identical.
• Matter could not be created or destroyed.
• J. J. Thompson discovered the subatomic particle (particles smaller than atoms).
• Thompson experimented to find negatively charged particles called electrons.

###Theories of the Atom

• Atoms contain electrons that are negatively charged particles. -The electrons sit inside a positively charged sphere, described as the "raisin bun" model.
• In 1912, Ernest Rutherford discovered the nucleus as the centre of the atom and discussed the proton, a positively charged particle, and believed electrons travelled around the nucleus.
• In 1913, Neils Bohr discovered electron shells.
  • Electrons travel around the nucleus in orbits with fixed distances.
  • Electrons can jump from shell to shell by losing or gaining energy.
• The current atomic theory states:
  • Atoms are composed of electrons (-), protons (+), and neutrons (neutral).
  • Protons and neutrons are found in the nucleus, while electrons circle it.
  • In stable atoms, the number of protons and electrons is equal.
  • The number of protons an atom has determines the element and identifies the atomic number.
  • The combined number of protons and neutrons tells the atomic mass.
    • Valence electrons are the outermost electrons of an atom.

Test your knowledge of the periodic table. This quiz covers topics such as organization, properties of elements, atomic structure, and reactivity. Learn about metals, non-metals, and metalloids and their placement on the periodic table.