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- [Instructor] We know that[br]everything in the universe

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is composed of atoms,

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but not all atoms are the same.

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There are many different types[br]of atoms called elements,

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each with a unique set of[br]physical and chemical properties.

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Many elements are[br]probably familiar to you.

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Oxygen and carbon, for[br]example, are elements,

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and so is gold.

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Others may be less familiar

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such as bismuth, xenon, and osmium.

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A particular element is identified

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by the number of protons in its atoms.

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And the number of protons[br]in the nucleus of an atom

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is its atomic number,[br]represented by the symbol Z.

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For example, helium has[br]an atomic number of two.

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That means that every[br]helium atom has two protons.

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And here's another example, iron,

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its atomic number is 26,

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so every iron atom has 26 protons.

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An element's atomic[br]number can also tell us

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the number of electrons in a[br]neutral atom of an element.

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Remember, equal and opposite[br]charges cancel each other out

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so to be neutral,

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an atom must have an[br]equal number of protons,

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which have a charge of 1+,

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and electrons, which have a charge of 1-.

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This means that our helium[br]atom must have two electrons

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and our iron atom must have 26 electrons.

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All of the known elements

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are organized according[br]to their atomic numbers

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in the periodic table.

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The periodic table lists the elements

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in order of increasing atomic number

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as you go from left to right[br]and from top to bottom.

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The elements are further[br]organized into columns

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based on their properties.

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Elements in the same column

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tend to have similar physical[br]and chemical properties.

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Every element is represented[br]by a chemical symbol,

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a unique one or two letter abbreviation

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that appears below the[br]element's atomic number

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on the periodic table.

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Many chemical symbols

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are based on the English[br]name for an element.

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For example, the symbol for hydrogen is H,

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and the symbol for aluminum is Al.

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But some chemical symbols

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are based on the Latin[br]name for the element.

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For example, the symbol for lead is Pb,

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which actually comes from[br]its Latin name plumbum.

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Notice that whenever the chemical symbol

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for an element has two letters,

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the second letter is written in lowercase.

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All of this information is contained

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inside of each element's[br]box on the periodic table.

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For example, here's the box[br]for the element nitrogen.

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At the top of the box

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is nitrogen's atomic[br]number, which is seven.

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Remember that this is equal

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to the number of protons[br]in each atom of nitrogen

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as well as the number of electrons.

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Below that is nitrogen's[br]chemical symbol, N,

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followed by its name.

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Often, you'll also see another number

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listed at the bottom of an elements box,

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which has to do with atomic mass.

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We'll cover details about[br]this and another video.

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What's neat about having

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all of this information in one place

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is that if we know one[br]detail about an element,

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either it's atomic number,[br]chemical symbol, or a name,

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we can often use the periodic table

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to find out the other details.

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Let's take a look at a few examples.

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Say we have the element phosphorus,

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what is its atomic number[br]and chemical symbol?

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Looking through the periodic table,

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we can find phosphorus

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and see that its atomic number is 15

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and its chemical symbol is P.

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Let's do another example.

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Say we know the chemical symbol Hg,

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what is this element's name

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and how many protons does it have?

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Here is the symbol Hg[br]on the periodic table.

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Its name is mercury,

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and its atomic number is 80

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so it has 80 protons.

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Let's reveal.

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The universe is made up

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of different types of[br]atoms called elements,

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and these elements are[br]organized by atomic number

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in the periodic table.

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So, the next time that you[br]stare up at the starry sky,

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you know that everything out[br]there is made up of elements.