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  • professor Dave here let's talk about types that matter

  • matter is anything that has mass

  • and occupies space. it can have many forms. we will commonly divide matter into

  • three phases

  • solid liquid and gas. we are probably familiar with these terms

  • let's define them anyway. a solid has fixed

  • shape and volume, the particles are touching and do not move

  • a liquid has fixed volume but no fixed shape

  • it will mold to its container. the particles are still touching

  • but they do move fluidly. a gas has no fixed volume

  • or fixed shape. it will completely fill its container. the particles are far apart

  • moving freely, and seldom touch. matter will frequently change forms

  • and describing these changes is at the heart of chemistry. a physical change

  • is one in which the chemical composition of the substance is

  • unchanged. when ice melts water is going from the solid phase

  • to the liquid phase. the way the water molecules are arranged

  • changes but they are still water molecules. a chemical change

  • is one in which the chemical composition of the substance does change

  • chemical bonds between atoms must break and form

  • to generate completely new substances. here

  • hydrogen gas and oxygen gas combine to form water

  • notice that hydrogen and oxygen used to be connected to themselves

  • and are now connected to each other. new bonds

  • new substance, chemistry has occurred

  • so things like a substance changing from one phase to another

  • are always physical changes. but if we make an entirely new substance with new

  • chemical bonds

  • thats a chemical change. a pure substance

  • is one that can't be separated into other materials

  • by any physical process. water whether you boil

  • or freeze it will still be water. it's a type of molecule

  • which is just multiple connected atoms. an element can't be broken down into

  • smaller parts by physical

  • or chemical means. for example water is not an element

  • it's a compound because it is made up two or more

  • elements, in this case oxygen and hydrogen. by a chemical process we can

  • divide water into these two elements

  • but that's as far as we can go with chemistry. these are now molecules

  • of a given element. a mixture is made of two or more

  • pure substances and these can be separated by physical processes

  • if you boil salt water the water will evaporate

  • and the salt won't so the substances will have separated

  • a mixture can be homogeneous meaning all the substances

  • are distributed evenly and every section looks the same

  • like sugar and water, or they can be heterogeneous

  • meaning they are not distributed evenly and zooming in on different sections

  • would look differently like oil and water.

  • we've got pure substances which can be elements made of only one type of atom

  • or compounds which are made of different types of atoms

  • but are still just one type of molecule.

  • or we can have mixtures which are made of multiple types of molecules

  • and are arranged in either homogeneous or heterogeneous fashion. let's check

  • comprehension

  • thanks for watching guys. subscribe to my channel for more tutorials

  • and as always feel free to email me

professor Dave here let's talk about types that matter


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B1 中級

物質的類型。元素、化合物和混合物 (Types of Matter: Elements, Compounds, and Mixtures)

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    Yrchinese 發佈於 2021 年 01 月 14 日