Law of conservation of mass

law of conservation of mass

• law of conservation of mass

• law of definite proportions

• law of multiple proportions

Explain the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.

• Explain the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.

• Summarize the five essential points of Dalton’s atomic theory.

• Explain the relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.

Atoms were indivisible and indestructible

• Atoms were indivisible and indestructible

Law of conservation of mass

• Law of conservation of mass

• mass is neither created nor destroyed during ordinary chemical reactions or physical changes

2. Law of definite proportions

• 2. Law of definite proportions

• a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source

• 3. Law of multiple proportions

• two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

Dalton transformed Democritus’s ideas on atoms into a scientific theory.

• Dalton transformed Democritus’s ideas on atoms into a scientific theory.

• Dalton used experimental methods not just philosophy

• Studied ratio in which elements combine in chemical reactions

All elements are composed of extremely small particles called atoms.

• All elements are composed of extremely small particles called atoms.

• Atoms of an element are identical in size, mass and other properties; atoms of different elements differ in size, mass, and other properties.

3. Atoms cannot be subdivided, created, or destroyed (law of conservation of mass)

• 3. Atoms cannot be subdivided, created, or destroyed (law of conservation of mass)

• 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. (law of definite proportions and multiple proportions)

• 5. In chemical reactions, atoms are combined, separated, or rearranged. (law of conservation of mass)

Moving Atoms: Making the World's Smallest Movie

• Moving Atoms: Making the World's Smallest Movie

Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that:

• Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that:

atom

• atom

• nuclear force

Summarize the observed properties of cathode rays that led to the discovery of the electron.

• Summarize the observed properties of cathode rays that led to the discovery of the electron.

• Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus.

• List the properties of protons, neutrons, and electrons.

• Define atom.

• Describe nuclear forces

One change to Dalton’s atomic theory - atoms ARE divisible

• One change to Dalton’s atomic theory - atoms ARE divisible

• Into subatomic particles:

• Electrons, protons, and neutrons

Cathode ray tube (CRT) is a vacuum tube containing an electron gun (source of electrons) and fluorescent screen used to view images. It accelerates and deflects the electron beam onto fluorescent screen to create images. Can be found in everyday devises such as televisions, video games, computers, video cameras, monitors, automated teller machines, oscilloscopes, and radar displays.

• Cathode ray tube (CRT) is a vacuum tube containing an electron gun (source of electrons) and fluorescent screen used to view images. It accelerates and deflects the electron beam onto fluorescent screen to create images. Can be found in everyday devises such as televisions, video games, computers, video cameras, monitors, automated teller machines, oscilloscopes, and radar displays.

• CRTs have been superseded by more modern display technologies such as LCD, plasma display, and OLED, which as of 2012 offer lower manufacturing and distribution costs.

Credited by many for the discovery of the existence of protons

• Credited by many for the discovery of the existence of protons

• discoverer of anode rays (canal rays)

• Worked in Berlin and Potsdam Observatories

Experimental evidence:

• Experimental evidence:

• atom mostly empty space
• almost all mass in nucleus
• e- distributed around nucleus…occupy most of the volume
• called “nuclear model”

An atom is the smallest particle of an element that retains the chemical properties of that element.

• An atom is the smallest particle of an element that retains the chemical properties of that element.

• The nucleus is a very small region located at the center of an atom.

• The nucleus is made up of at least one positively charged particle called a proton and usually one or more neutral particles called neutrons.

Surrounding the nucleus is a region occupied by negatively charged particles called electrons.

• Surrounding the nucleus is a region occupied by negatively charged particles called electrons.

• Protons, neutrons, and electrons are often referred to as subatomic particles.

• Atoms are electrically neutral because they contain equal numbers of protons and electrons

• The nuclei of atoms of different elements differ in their number of protons and therefore in the amount of positive charge they possess.

• Thus, the number of protons determines that atom’s identity.

atomic number

• atomic number

• isotope

• mass number

• nuclide

• unified atomic mass unit

Dalton wrong about elements of same type being identical…

• Dalton wrong about elements of same type being identical…

• Element’s atoms can have different # neutrons.

• different mass #
• Isotopes
• (flavors)

Frederick Soddy (1877-1956)

• Frederick Soddy (1877-1956)

• proposed idea of isotopes in 1912

• Isotopes - atoms of same element with different masses, because varying #s of neutrons

• 1921 Nobel Prize in Chemistry
• crater w/ his name on far side of Moon

We can also put mass number with a hyphen after name of element:

• We can also put mass number with a hyphen after name of element:

• carbon-12
• carbon-14
• uranium-235
• uranium-238

Atomic Mass Unit (amu)

• Atomic Mass Unit (amu)

• one-twelfth mass of C-12 atom

• Carbon-12 chosen b/c of its isotope purity

• Each isotope has own atomic mass

• we determine average from % abundance.

How heavy is an oxygen atom?

• How heavy is an oxygen atom?

• Depends, b/c different kinds of oxygen atoms exist.

• We’re more concerned with average atomic mass.

• Based on abundance (%) of each variety of that element in nature.

• Don’t use grams - #’s tooooo small

Multiply atomic mass of each isotope by abundance (decimal), then add results.

• Multiply atomic mass of each isotope by abundance (decimal), then add results.

• If not told otherwise, mass of isotope expressed in atomic mass units (amu)