1. Xo
   O
2. H2O
   Og

Oxygen is the third-most abundant element in the universe, the second-most abundant element in the Earth's atmosphere, and the most abundant element in the Earth's crust. It could be considered the most important element on Earth.

1. Hg
   HdR
2. H
   HR

The periodic symbol for hydrogen is "H" and it has the atomic number 1, which means its nucleus has just one proton. It is the most abundant element in the universe and it's what the Sun is made out of. Water, H2O, is made up of 2 hydrogen atoms bonded to one oxygen atom, so you can find plenty of hydrogen in the ocean.

1. Radon
   Ytterbium
2. Zirconium
   Rubidium

The periodic symbol for zirconium is "Zr," and it can form into zirconium dioxide (ZrO2), which is commonly known as zirconia and is a popular alternative to diamonds. Zirconia has a high optical density and is usually colorless.

1. Hn
   Hm
2. Hl
   He

The periodic symbol for Helium is "He" and it is second only to hydrogen as most abundant element in the universe. It is atomic number 2, which means its nucleus has just two protons. It is used to inflate balloons and blimps.

1. Ds
   Na
2. Dn
   SdM

The periodic symbol for sodium is "Na" and it's a silvery-white metal found in several forms on Earth, including rock salt, which is the mineral form of sodium chloride (NaCl), which is what the salt we commonly pour on our food is made out of. It is highly water-soluble and is one of the most dissolved elements in the oceans.

1. Titanium
   Tantalum
2. Tin
   Tungsten

The periodic symbol for titanium is "Ti" and titanium is one of the strongest metals on the planet. It's resistant to corrosion in sea water, chlorine and aqua regia, which is a fuming mixture of nitric and hydrochloric acid used to dissolve metals.

1. Nk
   Ni
2. Nl
   Nck

The periodic symbol for nickel is "Ni" and a five-cent nickel is made of 75% copper and 25% nickel. Nickel is also the second-most abundant element in the Earth's core. It's a silvery metal that is found in everything from zippers to cell phones.

1. Sulfur
   Selenium
2. Sodium
   Silicon

The periodic symbol for silicon is "Si" and it makes up more than 27% of the Earth's crust, which makes it the crust's second-most abundant element after oxygen. Silicon can be found in things like pieces of plastic and grains of sand.

1. Ag
   Au
2. Gl
   Gd

The periodic symbol for gold is "Au" and in 2019 it was worth more than $1,200 per ounce. Gold is found all over the world except for Antarctica, and the most gold sits in the oceans. The Witwatersrand Basin in South Africa is said to be the one of the most abundant gold reserves ever discovered.

1. Lead
   Wood
2. Steel
   Aluminum

The periodic symbol for lead is "Pb" and it is one of the softest metals on Earth. It is pretty dense but still really malleable and is a toxin that accumulates in human tissue and bones. Lead poisoning affects the nervous system and can cause brain damage. That's why lead paint, or lead in water, is so dangerous.

1. Zinc
   Potassium
2. Iron
   Calcium

The periodic symbol for iron is "Fe" and it makes up most of Earth's outer and inner core. Iron is the element that took humans out of the Bronze Age and into the Iron Age. An adult human body contains about four grams of iron.

1. K
   Pm
2. Tm
   P

The periodic symbol for potassium is "K" and potassium deficiency can lead to fatigue, weakness, nausea and a few other problems. Potassium makes up close to 2% of the Earth's crust, but is never found in free form. Potassium metal is so soft it can be cut with a knife.

1. N
   Ni
2. NI
   Nr

The periodic symbol for nitrogen is "N" and it's the most abundant element in the atmosphere. It was isolated and discovered by a Scottish physician in 1772 and named by a French chemist in 1790. It's essential in fostering the growth of plants.

1. Sulfur
   Uranium
2. Radium
   Argon

The periodic symbol for uranium is "U" and it is a silvery metal that is rarely found in nature. The most common use for uranium today is in the use of nuclear weaponry. Exposure and inhalation of uranium can cause major defects in humans.

1. Plutonium
   Platinum
2. Polonium
   Boron

The periodic symbol for plutonium is "Pu" and the atom bomb that was dropped on Nagasaki in 1945 was made with a plutonium core. It is a dangerous metal used for explosives and exposure to it is extremely dangerous and can lead to radiation poisoning, cancer or death.

1. Aluminum
   Arsenic
2. Astatine
   Actinium

The periodic symbol for arsenic is "As" and it's a potent poison. The Agency for Toxic Substances and Disease Registry considers it extremely hazardous. It is usually found in minerals within the Earth's crust and is rarely found in free form.

1. Ne
   En
2. Nx
   N

The periodic symbol for neon is "Ne" and it is the fifth-most abundant element in the universe after hydrogen, helium, oxygen and carbon. Although it's abundant in space, it is extremely rare on Earth because it is lighter than air and isn't able to bond to any solids. It is a colorless and odorless gas.

1. Cr
   Sc
2. Kr
   Ba

The periodic symbol for krypton is "Kr" and it is the name of the fake planet Krypton where Superman's weakness—kryptonite—comes from. In real life krypton is a colorless, odorless and tasteless gas that can be found is very small amounts in Earth's atmosphere.

1. Pu
   Cl
2. Li
   H

The periodic symbol for chlorine is "Cl" and it's a pale yellow-green gas that's commonly used in disinfectants. Chlorine in the form of chloride ions is essential for every living thing, and chlorine in the form of gas has been used as a deadly weapon in wars around the world.

1. Dr
   Rh
2. RhM
   R

The periodic symbol for rhodium is "Rh" and it's one of the rarest metals on Earth. Rhodium, along with gold, silver, platinum and others, is a noble metal that is resistant to corrosion. It is naturally found on its own.

1. Rn
   Li
2. Xe
   Nb

The periodic symbol for lithium is "Li" and it is a soft, silvery metal that is never found alone on Earth. It is the lightest metal and lightest solid element in the world. It is found in everyday items like batteries, lubricants, ceramics and even pharmaceuticals.

1. Ad
   As
2. At
   Af

The periodic symbol for astatine is "At" and it is the rarest naturally-occurring element on Earth. It is produced from the decay of other elements and is so radioactive that any visible piece would instantly vaporize.

1. Floridium
   Californium
2. Alasakiomium
   Coloradium

The periodic symbol for californium is "Cf" and it was discovered at the University of California Radiation Laboratory. It is named after the state of California. It is used for very specific cases like detecting gold and silver and cancer treatments.

1. Caesium
   Cobalt
2. Calcium
   Carbon

The periodic symbol for calcium is "Ca" and it is the third most abundant metal on Earth behind iron and aluminum. It is the most abundant metal in the human body and in nature it is most commonly found in limestone.

1. A
   An
2. Gr
   Ar

The periodic symbol for argon is "Ar" and it's the third most abundant gas in the atmosphere and the most abundant gas in the Earth's crust. It is a colorless gas that produces a purple glow when in an electric field.

1. Cobalt
   Calcium
2. Caesium
   Cerium

The periodic symbol for caesium is "Cs" and it is the softest metal on the periodic table. It melts slightly above room temperature. Its official melting point is 83.3 degrees Fahrenheit and its appearance is pale gold.

1. C
   Cp
2. Pr
   Cu

The periodic symbol for copper is "Cu" and pennies are 2.5% copper and 95% zinc. From 1793 to 1837 the penny was 100% copper, and between 1837 and 1982, the penny was always majority copper. All pennies made after 1982 only have a small amount of copper.

1. Ne
   Pt
2. Fe
   Co

The periodic symbol for platinum is "Pt" and it is one of the most expensive metals found on Earth. It is rather scarce in the Earth's crust and about 80% of the the metal's production occurs in South Africa. It is a silvery-white, lustrous metal.

1. H
   Ti
2. Sn
   TI

The periodic symbol for tin is "Sn" and it's pretty scarce on Earth. A large percentage is in Southeast Asia and it is produced from naturally-occurring deposits in Earth. It is used on all types of items to coat other metals and prevent corrosion.

1. Hg
   M
2. Mc
   Mr

The periodic symbol for mercury is "Hg" and it's a liquid metal that is commonly known as quicksilver. At standard conditions it is a heavy, silvery, metallic liquid and it's commonly used in thermometers and fluorescent lighting.

1. S
   H
2. O
   P

The periodic symbol for sulfur is "S" and it is a bright-yellow, crystalline solid. It is the fifth-most common element on Earth and it's used in everyday items like furniture, fertilizer and pesticides. An active volcano in Indonesia called Ijen is one of the most popular sites to mine sulfur.

1. Hg
   O
2. H
   Rn

The periodic symbol for radon is "Rn" and it is said to be the second-leading cause of cancer behind cigarette smoking. It is extremely rare since it is produced from the decay of other elements and then decays itself rather quickly.

1. Titanium
   Tungsten
2. Aluminum
   Steel

The periodic symbol for tungsten is "W" and it has the highest melting point (6,192 degrees Fahrenheit) and boiling point (10,706 degrees Fahrenheit) of any element. It also has the highest tensile strength of any metal, which means it requires the most strength to pull apart. It is, however, extremely brittle making it difficult to work with. It shatters almost immediately on impact.

1. Tungsten
   Tantalum
2. Thallium
   Titanium

The periodic symbol for thallium is "TI." Thallium is found in trace amounts in the Earth's crust and is mostly used in things like camera lenses and fiber optics. It is toxic and harmful to humans and can be lethal, even in small doses.

1. Copper
   Bronze
2. Gold
   Silver

The periodic symbol for silver is "Ag" and both gold and silver Olympic medals are actually 92% silver. Gold medals are then covered with at least six grams of gold. An ounce of silver is worth about $15 in 2019.